diff --git a/kadai1/tanaka0325/README.md b/kadai1/tanaka0325/README.md
new file mode 100644
index 0000000..c04f8c5
--- /dev/null
+++ b/kadai1/tanaka0325/README.md
@@ -0,0 +1,60 @@
+# Image Converter
+
+## Spec
+
+```
+## 次の仕様を満たすコマンドを作って下さい
+
+- ディレクトリを指定する
+- 指定したディレクトリ以下のJPGファイルをPNGに変換（デフォルト）
+- ディレクトリ以下は再帰的に処理する
+- 変換前と変換後の画像形式を指定できる（オプション）
+
+## 以下を満たすように開発してください
+
+- mainパッケージと分離する
+- 自作パッケージと標準パッケージと準標準パッケージのみ使う
+- 準標準パッケージ：golang.org/x以下のパッケージ
+- ユーザ定義型を作ってみる
+- GoDocを生成してみる
+- Go Modulesを使ってみる
+```
+
+## Usage
+
+```zsh
+# build
+$ cd imgconv
+$ go build -o imgconv ./cmd/imgconv
+
+# display help
+$ ./imgconv -h
+Usage of ./imgconv:
+  -f string
+        file extention before convert (default "jpg")
+  -n    dry run
+  -t string
+        file extention after convert (default "png")
+
+# single directory
+$ ./imgconv testdata/images
+
+# multi directories
+$ ./imgconv testdata/images testdata/images2
+
+# customize ext
+$ ./imgconv -f png -t gif testdata/images
+
+# dry run
+$ ./imgconv -n testdata/images testdata/images2
+testdata/images/sample1.jpg => testdata/images/sample1.png
+testdata/images2/img/sample3.jpg => testdata/images2/img/sample3.png
+testdata/images2/sample2.jpg => testdata/images2/sample2.png
+
+```
+
+## 感想
+
+- long option(?) はどうやってやれば良いのだろうか
+- そもそも作りとしてこれで良いのだろうか・・・めっちゃ悩みました
+
diff --git a/kadai1/tanaka0325/imgconv/args.go b/kadai1/tanaka0325/imgconv/args.go
new file mode 100644
index 0000000..4212901
--- /dev/null
+++ b/kadai1/tanaka0325/imgconv/args.go
@@ -0,0 +1,19 @@
+package imgconv
+
+// Args is type for command line arguments.
+type Args []string
+
+func (args Args) uniq() []string {
+	m := map[string]bool{}
+	u := []string{}
+
+	for _, v := range args {
+		if !m[v] {
+			m[v] = true
+
+			u = append(u, v)
+		}
+	}
+
+	return u
+}
diff --git a/kadai1/tanaka0325/imgconv/cmd/imgconv/main.go b/kadai1/tanaka0325/imgconv/cmd/imgconv/main.go
new file mode 100644
index 0000000..875aefa
--- /dev/null
+++ b/kadai1/tanaka0325/imgconv/cmd/imgconv/main.go
@@ -0,0 +1,30 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/gopherdojo/dojo8/kadai1/tanaka0325/imgconv"
+)
+
+var options imgconv.Options
+var args imgconv.Args
+
+func init() {
+	options.From = flag.String("f", "jpg", "file extension before convert")
+	options.To = flag.String("t", "png", "file extension after convert")
+	options.DryRun = flag.Bool("n", false, "dry run")
+	flag.Parse()
+
+	args = flag.Args()
+}
+
+func main() {
+	if err := imgconv.Run(options, args); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	os.Exit(0)
+}
diff --git a/kadai1/tanaka0325/imgconv/cnv_image.go b/kadai1/tanaka0325/imgconv/cnv_image.go
new file mode 100644
index 0000000..869a7d9
--- /dev/null
+++ b/kadai1/tanaka0325/imgconv/cnv_image.go
@@ -0,0 +1,81 @@
+package imgconv
+
+import (
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"io"
+
+	"golang.org/x/image/bmp"
+	"golang.org/x/image/tiff"
+)
+
+type Decoder interface {
+	Decode(io.Reader) (image.Image, error)
+}
+
+type Encoder interface {
+	Encode(io.Writer, image.Image) error
+}
+
+type DecodeEncoder interface {
+	Decoder
+	Encoder
+}
+
+type CnvImage struct{}
+
+// CnvImagePng is type for png format.
+type CnvImagePNG CnvImage
+
+func (ip CnvImagePNG) Decode(r io.Reader) (image.Image, error) { return png.Decode(r) }
+
+func (ip CnvImagePNG) Encode(w io.Writer, i image.Image) error { return png.Encode(w, i) }
+
+// CnvImageJPEG is type for jpeg format.
+type CnvImageJPEG CnvImage
+
+func (ip CnvImageJPEG) Decode(r io.Reader) (image.Image, error) { return jpeg.Decode(r) }
+
+func (ip CnvImageJPEG) Encode(w io.Writer, i image.Image) error { return jpeg.Encode(w, i, nil) }
+
+// CnvImageGIF is type for gif format.
+type CnvImageGIF CnvImage
+
+func (ip CnvImageGIF) Decode(r io.Reader) (image.Image, error) { return gif.Decode(r) }
+
+func (ip CnvImageGIF) Encode(w io.Writer, i image.Image) error {
+	return gif.Encode(w, i, &gif.Options{NumColors: 256})
+}
+
+// CnvImageBMP is type for bmp format.
+type CnvImageBMP CnvImage
+
+func (ip CnvImageBMP) Decode(r io.Reader) (image.Image, error) { return bmp.Decode(r) }
+
+func (ip CnvImageBMP) Encode(w io.Writer, i image.Image) error { return bmp.Encode(w, i) }
+
+// CnvImageTIFF is type for tiff format.
+type CnvImageTIFF CnvImage
+
+func (ip CnvImageTIFF) Decode(r io.Reader) (image.Image, error) { return tiff.Decode(r) }
+
+func (ip CnvImageTIFF) Encode(w io.Writer, i image.Image) error { return tiff.Encode(w, i, nil) }
+
+func newCnvImage(ext string) DecodeEncoder {
+	switch ext {
+	case "png":
+		return &CnvImagePNG{}
+	case "jpg", "jpeg":
+		return &CnvImageJPEG{}
+	case "gif":
+		return &CnvImageGIF{}
+	case "bmp":
+		return &CnvImageBMP{}
+	case "tiff", "tif":
+		return &CnvImageTIFF{}
+	}
+
+	return nil
+}
diff --git a/kadai1/tanaka0325/imgconv/go.mod b/kadai1/tanaka0325/imgconv/go.mod
new file mode 100644
index 0000000..ad64074
--- /dev/null
+++ b/kadai1/tanaka0325/imgconv/go.mod
@@ -0,0 +1,5 @@
+module github.com/gopherdojo/dojo8/kadai1/tanaka0325/imgconv
+
+go 1.14
+
+require golang.org/x/image v0.0.0-20200618115811-c13761719519
diff --git a/kadai1/tanaka0325/imgconv/go.sum b/kadai1/tanaka0325/imgconv/go.sum
new file mode 100644
index 0000000..394251b
--- /dev/null
+++ b/kadai1/tanaka0325/imgconv/go.sum
@@ -0,0 +1,3 @@
+golang.org/x/image v0.0.0-20200618115811-c13761719519 h1:1e2ufUJNM3lCHEY5jIgac/7UTjd6cgJNdatjPdFWf34=
+golang.org/x/image v0.0.0-20200618115811-c13761719519/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
diff --git a/kadai1/tanaka0325/imgconv/imgconv.go b/kadai1/tanaka0325/imgconv/imgconv.go
new file mode 100644
index 0000000..e80c35c
--- /dev/null
+++ b/kadai1/tanaka0325/imgconv/imgconv.go
@@ -0,0 +1,116 @@
+// Imgconv package is to convert images file format.
+package imgconv
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+var allowedExts = []string{"png", "jpg", "jpeg", "gif", "bmp", "tiff", "tif"}
+var fromExt string
+var toExt string
+
+// Run is to convert image file format.
+func Run(options Options, args Args) error {
+	// // validator
+	if err := options.validate(allowedExts); err != nil {
+		return err
+	}
+
+	fromExt = *options.From
+	toExt = *options.To
+
+	// get target image flepaths from args
+	paths, err := getTargetFilePaths(args, fromExt)
+	if err != nil {
+		return err
+	}
+
+	// convert
+	for _, path := range paths {
+		filename := strings.Replace(path, "."+fromExt, "", -1)
+		// "))
+		f := newCnvImage(fromExt)
+		t := newCnvImage(toExt)
+
+		if *options.DryRun {
+			fmt.Printf("%s.%s => %s.%s \n", filename, fromExt, filename, toExt)
+		} else if err := convert(f, t, filename); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func convert(d Decoder, e Encoder, filename string) (err error) {
+	// open file
+	r, err := os.Open(filename + "." + fromExt)
+	if err != nil {
+		return
+	}
+	defer r.Close()
+
+	// decode
+	img, err := d.Decode(r)
+	if err != nil {
+		return
+	}
+
+	// create file
+	w, err := os.Create(filename + "." + toExt)
+	if err != nil {
+		return err
+	}
+
+	defer func() {
+		err = w.Close()
+	}()
+
+	// encode
+	if err := e.Encode(w, img); err != nil {
+		return err
+	}
+
+	return
+}
+
+func getTargetFilePaths(args Args, from string) ([]string, error) {
+	uns := args.uniq()
+
+	paths := []string{}
+	for _, n := range uns {
+		if ok, err := isDir(n); err != nil {
+			return nil, err
+		} else if !ok {
+			return nil, fmt.Errorf("%s is not a directory", n)
+		}
+
+		if err := filepath.Walk(n, func(path string, info os.FileInfo, err error) error {
+			if filepath.Ext(path) == "."+from {
+				paths = append(paths, path)
+			}
+			return nil
+		}); err != nil {
+			return nil, err
+		}
+	}
+
+	return paths, nil
+}
+
+func isDir(path string) (bool, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return false, err
+	}
+
+	fi, err := f.Stat()
+	if err != nil {
+		return false, err
+	}
+
+	return fi.IsDir(), nil
+}
diff --git a/kadai1/tanaka0325/imgconv/options.go b/kadai1/tanaka0325/imgconv/options.go
new file mode 100644
index 0000000..e3e231c
--- /dev/null
+++ b/kadai1/tanaka0325/imgconv/options.go
@@ -0,0 +1,37 @@
+package imgconv
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// Options is type for command line options.
+type Options struct {
+	From   *string
+	To     *string
+	DryRun *bool
+}
+
+func (opt Options) validate(allowList []string) error {
+	to := strings.ToLower(*opt.To)
+	from := strings.ToLower(*opt.From)
+	targetExts := []string{to, from}
+
+	for _, e := range targetExts {
+		if err := include(allowList, e); err != nil {
+			return fmt.Errorf("%w. ext is only allowd in %s", err, allowList)
+		}
+	}
+
+	return nil
+}
+
+func include(list []string, w string) error {
+	for _, e := range list {
+		if e == w {
+			return nil
+		}
+	}
+	return errors.New(w + " is not allowed")
+}
diff --git a/kadai1/tanaka0325/imgconv/testdata/images/sample1.jpg b/kadai1/tanaka0325/imgconv/testdata/images/sample1.jpg
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diff --git a/kadai1/tanaka0325/imgconv/testdata/images2/img/sample3.jpg b/kadai1/tanaka0325/imgconv/testdata/images2/img/sample3.jpg
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diff --git a/kadai1/tanaka0325/imgconv/testdata/images2/sample2.jpg b/kadai1/tanaka0325/imgconv/testdata/images2/sample2.jpg
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