diff --git a/kadai1/tsubasaxzzz/main.go b/kadai1/tsubasaxzzz/main.go
new file mode 100644
index 0000000..44ac1dc
--- /dev/null
+++ b/kadai1/tsubasaxzzz/main.go
@@ -0,0 +1,42 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"myimage"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+var (
+	dir     = flag.String("dir", ".", "Target directory")
+	fromExt = flag.String("from-ext", "", "From extention")
+	toExt   = flag.String("to-ext", "", "To extention")
+)
+
+func main() {
+	flag.Parse()
+	startPath := filepath.Join(*dir)
+
+	fmt.Printf("Convert image file start.: target=[%s], from-extension=[%s], to-extension=[%s]\n", *dir, *fromExt, *toExt)
+
+	err := filepath.Walk(startPath,
+		func(path string, info os.FileInfo, err error) error {
+			// オプションで指定された拡張子のファイルの場合のみ
+			if strings.Replace(filepath.Ext(path), ".", "", 1) == *fromExt {
+				convfunc, err := myimage.GetConvertFunc(*fromExt, *toExt)
+				if err == nil {
+					fmt.Printf("Convert image file: filepath=[%s]\n", path)
+					convfunc(path)
+				} else {
+					fmt.Printf("Skip convert image file: filepath=[%s], reason=[%s]\n", path, err)
+				}
+			}
+			return err
+		})
+	if err != nil {
+		fmt.Printf("Error occured: error=[%s]\n", err)
+	}
+	fmt.Printf("Convert image file end.\n")
+}
diff --git a/kadai1/tsubasaxzzz/src/myimage/myimage.go b/kadai1/tsubasaxzzz/src/myimage/myimage.go
new file mode 100644
index 0000000..b1512d9
--- /dev/null
+++ b/kadai1/tsubasaxzzz/src/myimage/myimage.go
@@ -0,0 +1,78 @@
+package myimage
+
+import (
+	"errors"
+	"image/jpeg"
+	"image/png"
+	"os"
+	"path/filepath"
+)
+
+// 拡張子と対応する変換関数のマッピング
+var format = map[string]map[string]ConvertFunc{
+	"jpg": {
+		"png": jpg2png,
+	},
+	"jpeg": {
+		"png": jpg2png,
+	},
+	"png": {
+		"jpg": png2jpg,
+	},
+}
+
+// ConvertFunc is express of convert functions.
+type ConvertFunc func(path string) error
+
+// 拡張子削除関数
+func getFilePathWithoutExt(path string) string {
+	return path[:len(path)-len(filepath.Ext(path))]
+}
+
+// ----------------------------
+// 変換関数
+//-----------------------------
+// JPEG -> PNG
+func jpg2png(path string) error {
+	inFile, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	img, err := jpeg.Decode(inFile)
+	if err != nil {
+		return err
+	}
+
+	outFile, err := os.Create(getFilePathWithoutExt(path) + ".png")
+	if err != nil {
+		return err
+	}
+
+	return png.Encode(outFile, img)
+}
+
+// PNG -> JPG
+func png2jpg(path string) error {
+	inFile, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	img, err := png.Decode(inFile)
+	if err != nil {
+		return err
+	}
+	outFile, err := os.Create(getFilePathWithoutExt(path) + ".jpg")
+	if err != nil {
+		return err
+	}
+
+	return jpeg.Encode(outFile, img, &jpeg.Options{Quality: 100})
+}
+
+// GetConvertFunc is in order to get ConvertFunc by from and to extension.
+func GetConvertFunc(fromExt string, toExt string) (convfunc ConvertFunc, err error) {
+	if val, ok := format[fromExt][toExt]; ok {
+		return val, nil
+	}
+	return nil, errors.New("Convert function not found")
+}