diff --git a/mig/buyer.go b/mig/buyer.go
new file mode 100644
index 0000000..b80c498
--- /dev/null
+++ b/mig/buyer.go
@@ -0,0 +1,22 @@
+package mig
+
+type Buyer struct {
+	RoleDescription
+}
+
+func NewBuyer() *Buyer {
+	return &Buyer{
+		RoleDescription: RoleDescription{
+			Identifier: "0000000000",
+		},
+	}
+}
+
+func (buyer *Buyer) Validate() error {
+	err := buyer.RoleDescription.Validate()
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
diff --git a/mig/donate_mark.go b/mig/donate_mark.go
new file mode 100644
index 0000000..7f532bc
--- /dev/null
+++ b/mig/donate_mark.go
@@ -0,0 +1,22 @@
+package mig
+
+import "fmt"
+
+// DonateMarkEnum 捐贈註記 (表 4-11)
+type DonateMarkEnum string
+
+const (
+	// 非捐贈發票
+	DonateMarkNo DonateMarkEnum = "0"
+	// 捐贈發票
+	DonateMarkYes DonateMarkEnum = "1"
+)
+
+// Validate 檢查捐贈註記是否符合規範
+func (t DonateMarkEnum) Validate() error {
+	switch t {
+	case DonateMarkNo, DonateMarkYes:
+		return nil
+	}
+	return fmt.Errorf("捐贈註記 (DonateMark) 欄位格式錯誤")
+}
diff --git a/mig/f0401_test.go b/mig/f0401_test.go
new file mode 100644
index 0000000..d87a062
--- /dev/null
+++ b/mig/f0401_test.go
@@ -0,0 +1,132 @@
+package mig
+
+import (
+	"fmt"
+	"time"
+)
+
+func ExampleNewF0401Invoice() {
+	// 這是一個範例
+	// 這個範例是用來展示如何使用 NewF0401Invoice 來建立一個 F0401 發票物件
+	// 這個範例會建立一個空的 F0401 發票物件
+
+	// 首先，我們需要建立賣方資訊
+	seller := NewSeller()
+	seller.Identifier = "12345678"
+	seller.Name = "網路書店"
+	seller.Address = "台北市中正區和平西路一段 1 號"
+	seller.PersonInCharge = "王小明"
+	seller.EmailAddress = "wang@example.com"
+
+	// 接著，我們需要建立買方資訊
+	buyer := NewBuyer()
+	buyer.Identifier = "87654321"
+	buyer.Name = "網路購物者"
+	buyer.Address = "台北市信義區信義路五段 7 號"
+	buyer.PersonInCharge = "陳小美"
+	buyer.EmailAddress = "mei@example.com"
+
+	// 最後，我們需要建立發票明細
+	details := []*F0401ProductItem{}
+	item := NewF0401ProductItem("網紅小遙")
+	item.RelateNumber = "A1234567890"
+	item.Quantity = "1"
+	item.Unit = "個"
+	item.UnitPrice = "105"
+	item.Amount = "105"
+	details = append(details, item)
+
+	item = NewF0401ProductItem("30m USB 3.0 延長線")
+	item.RelateNumber = "A1234567891"
+	item.Quantity = "2"
+	item.Unit = "條"
+	item.UnitPrice = "210"
+	item.Amount = "420"
+	details = append(details, item)
+
+	// 現在，我們可以使用 NewF0401Invoice 來建立一個 F0401 發票物件
+	invoice, err := NewF0401Invoice(seller, buyer, details)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	invoice.Main.InvoiceNumber = "QQ18927486"
+	invoice.SetDateAndTime(time.Date(2024, 3, 2, 11, 39, 40, 0, time.Local))
+	invoice.Details.FillSequenceNumber()
+	invoice.FillAmount()
+
+	// 最後，我們可以檢查這個發票是否符合規範
+	if err := invoice.Validate(); err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	// Output:
+	f, err := invoice.Bytes()
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println(string(f))
+
+	// 這個範例會輸出一個符合 F0401 發票規範的 XML 字串
+	// Output:
+	// <Invoice xmlns="urn:GEINV:eInvoiceMessage:F0401:4.0">
+	// 	<Main>
+	// 		<InvoiceNumber>A1234567890</InvoiceNumber>
+	// 		<InvoiceDate>20210101</InvoiceDate>
+	// 		<InvoiceTime>00:00:00</InvoiceTime>
+	// 		<Seller>
+	// 			<Identifier>12345678</Identifier>
+	// 			<Name>網路書店</Name>
+	// 			<Address>台北市中正區和平西路一段 1 號</Address>
+	// 			<PersonInCharge>王小明</PersonInCharge>
+	// 			<EmailAddress>
+	// 				<
+	// 			</EmailAddress>
+	// 		</Seller>
+	// 		<Buyer>
+	// 			<Identifier>87654321</Identifier>
+	// 			<Name>網路購物者</Name>
+	// 			<Address>台北市信義區信義路五段 7 號</Address>
+	// 			<PersonInCharge>陳小美</PersonInCharge>
+	// 			<EmailAddress>
+	// 				<
+	// 			</EmailAddress>
+	// 		</Buyer>
+	// 		<InvoiceType>07</InvoiceType>
+	// 		<DonateMark>N</DonateMark>
+	// 		<PrintMark>Y</PrintMark>
+	// 	</Main>
+	// 	<Details>
+	// 		<SequenceNumber>1</SequenceNumber>
+	// 		<ProductItem>
+	// 			<Description>網紅小遙</Description>
+	// 			<Quantity>1</Quantity>
+	// 			<Unit>個</Unit>
+	// 			<UnitPrice>100</UnitPrice>
+	// 			<Amount>105</Amount>
+	// 			<RelateNumber>A1234567890</RelateNumber>
+	// 		</ProductItem>
+	// 		<SequenceNumber>2</SequenceNumber>
+	// 		<ProductItem>
+	// 			<Description>30m USB 3.0 延長線</Description>
+	// 			<Quantity>1</Quantity>
+	// 			<Unit>條</Unit>
+	// 			<UnitPrice>1550</UnitPrice>
+	// 			<Amount>1628</Amount>
+	// 			<RelateNumber>A1234567891</RelateNumber>
+	// 		</ProductItem>
+	// 	</Details>
+	// 	<Amount>
+	// 		<SalesAmount>1733</SalesAmount>
+	// 		<TaxType>1</TaxType>
+	// 		<TaxRate>0.05</TaxRate>
+	// 		<TaxAmount>83</TaxAmount>
+	// 		<TotalAmount>1816</TotalAmount>
+	// 		<FreeTaxSalesAmount>0</FreeTaxSalesAmount>
+	// 		<ZeroTaxSalesAmount>0</ZeroTaxSalesAmount>
+	// 	</Amount>
+	// </Invoice>
+
+}
diff --git a/mig/f0401invoice.go b/mig/f0401invoice.go
index a6685f5..4c5df5e 100644
--- a/mig/f0401invoice.go
+++ b/mig/f0401invoice.go
@@ -3,6 +3,8 @@ package mig
 import (
 	"encoding/xml"
 	"fmt"
+	"math/big"
+	"time"
 )
 
 type F0401Invoice struct {
@@ -16,7 +18,7 @@ type F0401Invoice struct {
 }
 
 // NewF0401Invoice 會回傳一個新的F0401發票，輸入參數有賣方資訊 (seller) 與買方資訊 (buyer)以及發票明細
-func NewF0401Invoice(seller *RoleDescription, buyer *RoleDescription, details []*F0401ProductItem) (*F0401Invoice, error) {
+func NewF0401Invoice(seller *Seller, buyer *Buyer, details []*F0401ProductItem) (*F0401Invoice, error) {
 
 	ret := &F0401Invoice{
 		Xmlns: "urn:GEINV:eInvoiceMessage:F0401:4.0",
@@ -24,24 +26,83 @@ func NewF0401Invoice(seller *RoleDescription, buyer *RoleDescription, details []
 
 	ret.Main = &F0401InvoiceMain{
 		InvoiceMain: InvoiceMain{
-			Seller: seller,
-			Buyer:  buyer,
+			InvoiceDate: time.Now().Format("20060102"),
+			InvoiceTime: time.Now().Format("15:04:05"),
+			Seller:      seller,
+			Buyer:       buyer,
+			InvoiceType: InvoiceTypeGeneral,
+			DonateMark:  DonateMarkNo,
 		},
+		PrintMark: "Y",
 	}
 
 	ret.Details = &F0401InvoiceDetail{
 		ProductItem: details,
 	}
 
-	amount := &F0401InvoiceAmount{}
-	for _, item := range details {
-		amount.SalesAmount += item.Amount
+	amount := &F0401InvoiceAmount{
+		InvoiceAmount: InvoiceAmount{
+			TaxRate: "0.05",
+			TaxType: TaxTypeTaxable,
+		},
+		FreeTaxSalesAmount: "0",
+		ZeroTaxSalesAmount: "0",
 	}
-	amount.TotalAmount = amount.SalesAmount
+
 	ret.Amount = amount
 	return ret, nil
 }
 
+func (invoice *F0401Invoice) SetDateAndTime(t time.Time) {
+	invoice.Main.InvoiceDate = t.Format("20060102")
+	invoice.Main.InvoiceTime = t.Format("15:04:05")
+}
+
+// IsB2C 會回傳發票是否為B2C發票，判斷根據 (表 4-7 BAN 資料元規格)
+func (invoice *F0401Invoice) IsB2C() bool {
+	return invoice.Main.Buyer.Identifier == "0000000000"
+}
+
+// FillAmount 會根據發票明細填入 SalesAmount, TaxAmount, TotalAmount
+// SalesAmount 為明細的金額加總
+// 當此發票為 B2B 發票時，TaxAmount 為 SalesAmount * TaxRate (四捨五入至整數)
+// 當此發票為 B2C 發票時，TaxAmount 為 0
+// TotalAmount 為 SalesAmount + TaxAmount
+func (invoice *F0401Invoice) FillAmount() error {
+	salesAmount := new(big.Float)
+	taxAmount := new(big.Float)
+	for _, item := range invoice.Details.ProductItem {
+		amount := new(big.Float)
+		amount, ok := amount.SetString(item.Amount)
+		if !ok {
+			return fmt.Errorf("parse amount failed")
+		}
+		salesAmount.Add(salesAmount, amount)
+	}
+	invoice.Amount.SalesAmount = salesAmount.Text('f', 0)
+
+	if invoice.IsB2C() {
+		invoice.Amount.TaxAmount = "0"
+	} else {
+		taxRate := new(big.Float)
+		taxRate, ok := taxRate.SetString(invoice.Amount.TaxRate)
+		if !ok {
+			return fmt.Errorf("parse tax rate failed")
+		}
+		taxAmount := new(big.Float).Mul(salesAmount, taxRate)
+
+		// 四捨五入至整數
+		taxAmount = taxAmount.Add(taxAmount, big.NewFloat(0.5))
+		bint, _ := taxAmount.Int(nil)
+		invoice.Amount.TaxAmount = bint.String()
+	}
+	taxAmount.SetString(invoice.Amount.TaxAmount)
+	totalAmount := new(big.Float)
+	totalAmount.Add(salesAmount, taxAmount)
+	invoice.Amount.TotalAmount = totalAmount.Text('f', 0)
+	return nil
+}
+
 func (invoice *F0401Invoice) Validate() error {
 	if invoice.Main == nil {
 		return fmt.Errorf("發票主要資訊為必填")
@@ -65,5 +126,5 @@ func (invoice *F0401Invoice) Validate() error {
 }
 
 func (f *F0401Invoice) Bytes() ([]byte, error) {
-	return xml.Marshal(f)
+	return xml.MarshalIndent(f, "", "  ")
 }
diff --git a/mig/invoice_amount.go b/mig/invoice_amount.go
index 1cd9410..5c62026 100644
--- a/mig/invoice_amount.go
+++ b/mig/invoice_amount.go
@@ -9,16 +9,16 @@ import "fmt"
 // 相同部分的驗證會在 InvoiceAmount 物件被驗證，如果規則有不同時則會被拆分驗證
 
 type InvoiceAmount struct {
-	Text                   string `xml:",chardata"`
-	SalesAmount            string `xml:"SalesAmount"`
-	TaxType                string `xml:"TaxType"`
-	TaxRate                string `xml:"TaxRate"`
-	TaxAmount              string `xml:"TaxAmount"`
-	TotalAmount            string `xml:"TotalAmount"`
-	DiscountAmount         string `xml:"DiscountAmount,omitempty"`
-	OriginalCurrencyAmount string `xml:"OriginalCurrencyAmount,omitempty"`
-	ExchangeRate           string `xml:"ExchangeRate,omitempty"`
-	Currency               string `xml:"Currency,omitempty"`
+	Text                   string      `xml:",chardata"`
+	SalesAmount            string      `xml:"SalesAmount"`
+	TaxType                TaxTypeEnum `xml:"TaxType"`
+	TaxRate                string      `xml:"TaxRate"`
+	TaxAmount              string      `xml:"TaxAmount"`
+	TotalAmount            string      `xml:"TotalAmount"`
+	DiscountAmount         string      `xml:"DiscountAmount,omitempty"`
+	OriginalCurrencyAmount string      `xml:"OriginalCurrencyAmount,omitempty"`
+	ExchangeRate           string      `xml:"ExchangeRate,omitempty"`
+	Currency               string      `xml:"Currency,omitempty"`
 }
 
 type A0101InvoiceAmount struct {
@@ -48,7 +48,10 @@ func (block *InvoiceAmount) Validate() error {
 	if block.TaxType == "" {
 		return fmt.Errorf("課稅別 (TaxType) 為必填")
 	}
-	// TODO: validate TaxType in TaxTypeEnum
+	err := block.TaxType.Validate()
+	if err != nil {
+		return err
+	}
 
 	if block.TaxRate == "" {
 		return fmt.Errorf("稅率 (TaxRate) 為必填")
diff --git a/mig/invoice_detail.go b/mig/invoice_detail.go
index 5865419..d7c4db6 100644
--- a/mig/invoice_detail.go
+++ b/mig/invoice_detail.go
@@ -26,9 +26,9 @@ func (block *A0101InvoiceDetail) Validate() error {
 		return fmt.Errorf("發票明細項目數量不得超過9999個，目前為%d", len)
 	}
 
-	for _, item := range block.ProductItem {
+	for i, item := range block.ProductItem {
 		if err := item.Validate(); err != nil {
-			return err
+			return fmt.Errorf("第 %d 個發票明細項目驗證錯誤: %v", i+1, err)
 		}
 	}
 	return nil
@@ -42,10 +42,22 @@ func (block *F0401InvoiceDetail) Validate() error {
 		return fmt.Errorf("發票明細項目數量不得超過9999個，目前為%d", len)
 	}
 
-	for _, item := range block.ProductItem {
+	for i, item := range block.ProductItem {
 		if err := item.Validate(); err != nil {
-			return err
+			return fmt.Errorf("第 %d 個發票明細項目驗證錯誤: %v", i+1, err)
 		}
 	}
 	return nil
 }
+
+func (block *A0101InvoiceDetail) FillSequenceNumber() {
+	for i, item := range block.ProductItem {
+		item.SequenceNumber = fmt.Sprintf("%d", i+1)
+	}
+}
+
+func (block *F0401InvoiceDetail) FillSequenceNumber() {
+	for i, item := range block.ProductItem {
+		item.SequenceNumber = fmt.Sprintf("%d", i+1)
+	}
+}
diff --git a/mig/invoice_main.go b/mig/invoice_main.go
index cb8a2f4..58e3757 100644
--- a/mig/invoice_main.go
+++ b/mig/invoice_main.go
@@ -10,11 +10,11 @@ import (
 
 // InvoiceMain represents the main information of an invoice.
 type InvoiceMain struct {
-	InvoiceNumber string           `xml:"InvoiceNumber"`
-	InvoiceDate   string           `xml:"InvoiceDate"`
-	InvoiceTime   string           `xml:"InvoiceTime"`
-	Seller        *RoleDescription `xml:"Seller"`
-	Buyer         *RoleDescription `xml:"Buyer"`
+	InvoiceNumber string  `xml:"InvoiceNumber"`
+	InvoiceDate   string  `xml:"InvoiceDate"`
+	InvoiceTime   string  `xml:"InvoiceTime"`
+	Seller        *Seller `xml:"Seller"`
+	Buyer         *Buyer  `xml:"Buyer"`
 
 	BuyerRemark           string `xml:"BuyerRemark,omitempty"`
 	MainRemark            string `xml:"MainRemark,omitempty"`
@@ -22,9 +22,9 @@ type InvoiceMain struct {
 	Category              string `xml:"Category,omitempty"`
 	RelateNumber          string `xml:"RelateNumber,omitempty"`
 
-	InvoiceType string `xml:"InvoiceType"`
-	GroupMark   string `xml:"GroupMark,omitempty"`
-	DonateMark  string `xml:"DonateMark"`
+	InvoiceType InvoiceTypeEnum `xml:"InvoiceType"`
+	GroupMark   string          `xml:"GroupMark,omitempty"`
+	DonateMark  DonateMarkEnum  `xml:"DonateMark"`
 
 	ZeroTaxRateReason string `xml:"ZeroTaxRateReason,omitempty"`
 	Reserved1         string `xml:"Reserved1,omitempty"`
@@ -114,7 +114,10 @@ func (block *InvoiceMain) Validate() error {
 	if block.InvoiceType == "" {
 		return fmt.Errorf("發票類別 (InvoiceType) 為必填")
 	}
-	// TODO: validate InvoiceType in InvoiceTypeEnum
+	err := block.InvoiceType.Validate()
+	if err != nil {
+		return fmt.Errorf("發票類別 (InvoiceType) 不符規範: %w", err)
+	}
 
 	if len(block.GroupMark) > 1 {
 		return fmt.Errorf("彙開註記 (GroupMark) 長度不得大於1個字元")
@@ -124,9 +127,7 @@ func (block *InvoiceMain) Validate() error {
 		return fmt.Errorf("捐贈註記 (DonateMark) 為必填")
 	}
 
-	if block.ZeroTaxRateReason == "" {
-		return fmt.Errorf("零稅率原因 (ZeroTaxRateReason) 為必填")
-	}
+	// TODO: validate ZeroTaxRateReason in ZeroTaxRateReasonEnum
 
 	if len(block.Reserved1) > 20 {
 		return fmt.Errorf("保留欄位 (Reserved1) 長度不得大於20個字元")
@@ -198,12 +199,14 @@ func (block *F0401InvoiceMain) Validate() error {
 		return fmt.Errorf("發票捐贈對象 (NPOBAN) 長度不得大於10個字元")
 	}
 
-	if len(block.RandomNumber) != 4 {
-		return fmt.Errorf("發票防偽隨機碼 (RandomNumber) 長度必須為4個字元")
-	}
-	pattern := "[0-9]{4}"
-	if match, _ := regexp.MatchString(pattern, block.RandomNumber); !match {
-		return fmt.Errorf("發票防偽隨機碼 (RandomNumber) 應為4位數字")
+	if block.RandomNumber != "" {
+		if len(block.RandomNumber) != 4 {
+			return fmt.Errorf("發票防偽隨機碼 (RandomNumber) 長度必須為4個字元")
+		}
+		pattern := "[0-9]{4}"
+		if match, _ := regexp.MatchString(pattern, block.RandomNumber); !match {
+			return fmt.Errorf("發票防偽隨機碼 (RandomNumber) 應為4位數字")
+		}
 	}
 
 	// TODO: validate BondedAreaConfirm in BondedAreaConfirmEnum
diff --git a/mig/invoice_type.go b/mig/invoice_type.go
new file mode 100644
index 0000000..a17f842
--- /dev/null
+++ b/mig/invoice_type.go
@@ -0,0 +1,22 @@
+package mig
+
+import "fmt"
+
+// InvoiceTypeEnum 電子發票類別 (表 4-4)
+type InvoiceTypeEnum string
+
+const (
+	// 一般稅額計算之電子發票
+	InvoiceTypeGeneral InvoiceTypeEnum = "07"
+	// 特種稅額計算之電子發票
+	InvoiceTypeSpecial InvoiceTypeEnum = "08"
+)
+
+// Validate 檢查發票類別是否符合規範
+func (t InvoiceTypeEnum) Validate() error {
+	switch t {
+	case InvoiceTypeGeneral, InvoiceTypeSpecial:
+		return nil
+	}
+	return fmt.Errorf("發票類別 (InvoiceType) 欄位格式錯誤")
+}
diff --git a/mig/main.go b/mig/main.go
index d0c8ed8..1675fff 100644
--- a/mig/main.go
+++ b/mig/main.go
@@ -5,18 +5,6 @@ import (
 	"log"
 )
 
-type RoleDescription struct {
-	Identifier      string `xml:"Identifier"`
-	Name            string `xml:"Name"`
-	Address         string `xml:"Address,omitempty"`
-	PersonInCharge  string `xml:"PersonInCharge,omitempty"`
-	TelephoneNumber string `xml:"TelephoneNumber,omitempty"`
-	FacsimileNumber string `xml:"FacsimileNumber,omitempty"`
-	EmailAddress    string `xml:"EmailAddress,omitempty"`
-	CustomerNumber  string `xml:"CustomerNumber,omitempty"`
-	RoleRemark      string `xml:"RoleRemark,omitempty"`
-}
-
 type C0401Invoice struct {
 	XMLName xml.Name `xml:"Invoice"`
 	Text    string   `xml:",chardata"`
@@ -33,7 +21,7 @@ func NewC0401Invoice(b []byte) (*C0401Invoice, error) {
 	if err := xml.Unmarshal(b, &f); err != nil {
 		log.Fatal(err)
 	}
-	log.Println("xmlname", f.XMLName.Space, f.XMLName.Local)
+	// log.Println("xmlname", f.XMLName.Space, f.XMLName.Local)
 
 	return &f, nil
 }
diff --git a/mig/main_test.go b/mig/main_test.go
index b4d4f0d..ea56bcb 100644
--- a/mig/main_test.go
+++ b/mig/main_test.go
@@ -16,16 +16,20 @@ func TestMarshalC0401(t *testing.T) {
 				InvoiceNumber: "AA00000000",
 				InvoiceDate:   "20060102",
 				InvoiceTime:   "15:04:05",
-				Seller: &RoleDescription{
-					Identifier:     "54834795",
-					Name:           "台灣智慧家庭股份有限公司",
-					Address:        "Address",
-					PersonInCharge: "PersonInCharge",
-					EmailAddress:   "example@example.com",
+				Seller: &Seller{
+					RoleDescription: RoleDescription{
+						Identifier:     "54834795",
+						Name:           "台灣智慧家庭股份有限公司",
+						Address:        "Address",
+						PersonInCharge: "PersonInCharge",
+						EmailAddress:   "example@example.com",
+					},
 				},
-				Buyer: &RoleDescription{
-					Identifier: "0000000000",
-					Name:       "Buyer Name",
+				Buyer: &Buyer{
+					RoleDescription: RoleDescription{
+						Identifier: "0000000000",
+						Name:       "Buyer Name",
+					},
 				},
 				InvoiceType: "07",
 				DonateMark:  "0",
diff --git a/mig/product_item.go b/mig/product_item.go
index 3a91de4..032e86b 100644
--- a/mig/product_item.go
+++ b/mig/product_item.go
@@ -24,7 +24,7 @@ type InvoiceProductItem struct {
 
 	Description string `xml:"Description"`
 
-	TaxType string `xml:"TaxType"`
+	TaxType TaxTypeEnum `xml:"TaxType"`
 
 	SequenceNumber string `xml:"SequenceNumber"`
 	Remark         string `xml:"Remark,omitempty"`
@@ -40,13 +40,22 @@ type AllowanceProductItem struct {
 	OriginalDescription     string `xml:"OriginalDescription"`
 	AllowanceSequenceNumber string `xml:"AllowanceSequenceNumber"`
 
-	TaxType string `xml:"TaxType"`
+	TaxType TaxTypeEnum `xml:"TaxType"`
 }
 
 type F0401ProductItem struct {
 	InvoiceProductItem
 }
 
+func NewF0401ProductItem(description string) *F0401ProductItem {
+	return &F0401ProductItem{
+		InvoiceProductItem{
+			Description: description,
+			TaxType:     TaxTypeTaxable,
+		},
+	}
+}
+
 func (item *ProductItem) Validate() error {
 
 	if item.Quantity == "" {
@@ -68,6 +77,8 @@ func (item *ProductItem) Validate() error {
 	}
 	// TODO: check Amount in type of decimal(20,7)
 
+	// TODO: check amount = quantity * unit price * (1 + tax rate)
+
 	return nil
 }
 
@@ -89,7 +100,10 @@ func (item *InvoiceProductItem) Validate() error {
 	if item.TaxType == "" {
 		return fmt.Errorf("課稅別 (TaxType) 為必填")
 	}
-	// TODO: validate TaxType in TaxTypeEnum
+	err = item.TaxType.Validate()
+	if err != nil {
+		return err
+	}
 
 	if item.SequenceNumber == "" {
 		return fmt.Errorf("明細排列序號 (SequenceNumber) 為必填")
@@ -144,7 +158,10 @@ func (item *AllowanceProductItem) Validate() error {
 	if item.TaxType == "" {
 		return fmt.Errorf("課稅別 (TaxType) 為必填")
 	}
-	// TODO: validate TaxType in TaxTypeEnum
+	err = item.TaxType.Validate()
+	if err != nil {
+		return err
+	}
 	return nil
 }
 
diff --git a/mig/role_description.go b/mig/role_description.go
new file mode 100644
index 0000000..c0a4441
--- /dev/null
+++ b/mig/role_description.go
@@ -0,0 +1,63 @@
+package mig
+
+import "fmt"
+
+type RoleDescription struct {
+	Identifier      string `xml:"Identifier"`
+	Name            string `xml:"Name"`
+	Address         string `xml:"Address,omitempty"`
+	PersonInCharge  string `xml:"PersonInCharge,omitempty"`
+	TelephoneNumber string `xml:"TelephoneNumber,omitempty"`
+	FacsimileNumber string `xml:"FacsimileNumber,omitempty"`
+	EmailAddress    string `xml:"EmailAddress,omitempty"`
+	CustomerNumber  string `xml:"CustomerNumber,omitempty"`
+	RoleRemark      string `xml:"RoleRemark,omitempty"`
+}
+
+// Validate 檢查賣方資料是否符合規範
+func (item *RoleDescription) Validate() error {
+	if item.Identifier == "" {
+		return fmt.Errorf("識別碼 (Identifier) 為必填")
+	}
+	// TODO: validate Identifier in type of BAN
+
+	if item.Name == "" {
+		return fmt.Errorf("名稱 (Name) 為必填")
+	}
+	if len(item.Name) < 1 {
+		return fmt.Errorf("名稱 (Name) 長度不得小於1個字元")
+	}
+	if len(item.Name) > 60 {
+		return fmt.Errorf("名稱 (Name) 長度不得大於60個字元")
+	}
+
+	if len(item.Address) > 100 {
+		return fmt.Errorf("地址 (Address) 長度不得大於100")
+	}
+
+	if len(item.PersonInCharge) > 30 {
+		return fmt.Errorf("負責人姓名 (PersonInCharge) 長度不得大於30個字元")
+	}
+
+	if len(item.TelephoneNumber) > 26 {
+		return fmt.Errorf("電話號碼 (TelephoneNumber) 長度不得大於26個字元")
+	}
+
+	if len(item.FacsimileNumber) > 26 {
+		return fmt.Errorf("傳真號碼 (FacsimileNumber) 長度不得大於26個字元")
+	}
+
+	if len(item.EmailAddress) > 400 {
+		return fmt.Errorf("電子郵件地址 (EmailAddress) 長度不得大於400個字元")
+	}
+
+	if len(item.CustomerNumber) > 20 {
+		return fmt.Errorf("客戶編號 (CustomerNumber) 長度不得大於20個字元")
+	}
+
+	if len(item.RoleRemark) > 40 {
+		return fmt.Errorf("營業人角色註記 (RoleRemark) 長度不得大於40個字元")
+	}
+
+	return nil
+}
diff --git a/mig/seller.go b/mig/seller.go
index 953f269..cb52ab9 100644
--- a/mig/seller.go
+++ b/mig/seller.go
@@ -2,60 +2,22 @@ package mig
 
 import "fmt"
 
-func NewSeller() *RoleDescription {
-	return &RoleDescription{}
+type Seller struct {
+	RoleDescription
 }
 
-// Validate 檢查賣方資料是否符合規範
-func (seller *RoleDescription) Validate() error {
-	if seller.Identifier == "" {
-		return fmt.Errorf("賣方識別碼(統一編號)為必填")
-	}
-	if len(seller.Identifier) > 10 {
-		// 通常統一編號長度為8個字元，但是規範最大值為10。
-		return fmt.Errorf("賣方識別碼(統一編號)長度不得大於10個字元")
-	}
+func NewSeller() *Seller {
+	return &Seller{}
+}
 
-	if seller.Name == "" {
-		return fmt.Errorf("賣方營業人名稱為必填")
-	}
-	if len(seller.Name) < 1 {
-		return fmt.Errorf("賣方營業人名稱長度不得小於1個字元")
-	}
-	if len(seller.Name) > 60 {
-		return fmt.Errorf("賣方營業人名稱長度不得大於60個字元")
+func (seller *Seller) Validate() error {
+	err := seller.RoleDescription.Validate()
+	if err != nil {
+		return err
 	}
 
 	if seller.Address == "" {
-		return fmt.Errorf("賣方地址欄位為必填")
-	}
-	if len(seller.Address) > 100 {
-		return fmt.Errorf("賣方營業地址長度不得大於100")
-	}
-
-	if len(seller.PersonInCharge) > 30 {
-		return fmt.Errorf("賣方負責人姓名長度不得大於30個字元")
-	}
-
-	if len(seller.TelephoneNumber) > 26 {
-		return fmt.Errorf("賣方電話號碼長度不得大於26個字元")
+		return fmt.Errorf("賣方地址欄位 (Address) 為必填")
 	}
-
-	if len(seller.FacsimileNumber) > 26 {
-		return fmt.Errorf("賣方傳真號碼長度不得大於26個字元")
-	}
-
-	if len(seller.EmailAddress) > 400 {
-		return fmt.Errorf("賣方電子郵件地址長度不得大於400個字元")
-	}
-
-	if len(seller.CustomerNumber) > 20 {
-		return fmt.Errorf("賣方客戶編號長度不得大於20個字元")
-	}
-
-	if len(seller.RoleRemark) > 40 {
-		return fmt.Errorf("賣方營業人角色註記長度不得大於40個字元")
-	}
-
 	return nil
 }
diff --git a/mig/tax_type.go b/mig/tax_type.go
new file mode 100644
index 0000000..dc712cd
--- /dev/null
+++ b/mig/tax_type.go
@@ -0,0 +1,26 @@
+package mig
+
+import "fmt"
+
+type TaxTypeEnum string
+
+const (
+	// 應稅
+	TaxTypeTaxable TaxTypeEnum = "1"
+	// 零稅率
+	TaxTypeZeroRated TaxTypeEnum = "2"
+	// 免稅
+	TaxTypeFreeTax TaxTypeEnum = "3"
+	// 應稅(特種稅率)
+	TaxTypeTaxableSpecial TaxTypeEnum = "4"
+	// 混合應稅與免稅或零稅率 (限訊息 F0401 使用)
+	TaxTypeMixed TaxTypeEnum = "9"
+)
+
+func (t TaxTypeEnum) Validate() error {
+	switch t {
+	case TaxTypeTaxable, TaxTypeZeroRated, TaxTypeFreeTax, TaxTypeTaxableSpecial, TaxTypeMixed:
+		return nil
+	}
+	return fmt.Errorf("課稅別 (TaxType) 欄位格式錯誤")
+}