diff --git a/kadai4/go.mod b/kadai4/go.mod
new file mode 100644
index 00000000..a71bfa85
--- /dev/null
+++ b/kadai4/go.mod
@@ -0,0 +1,3 @@
+module github.com/kotaaaa/gopherdojo-studyroom/kadai4
+
+go 1.14
diff --git a/kadai4/kotaaaa/README.md b/kadai4/kotaaaa/README.md
new file mode 100644
index 00000000..9dfb0e30
--- /dev/null
+++ b/kadai4/kotaaaa/README.md
@@ -0,0 +1,23 @@
+# Let's make a fortune API.
+- Returning omikuji results in JSON format
+- Only New Year's Day (Jan. 1 - Jan. 3) is set to "Daikichi".
+- Writing tests for the handler
+
+# How to use
+```
+$ go build -o fortune-api
+$ ./fortune-api 
+$ curl "http://localhost:8080/draw?p=2021-11-14"
+{"status":"Success","result":"末吉"}
+$ curl "http://localhost:8080/draw"
+{"status":"Success","result":"小吉"}
+```
+
+# How to Test
+```
+$ go test ./... --count=1 -cover
+?       github.com/kotaaaa/gopherdojo-studyroom/kadai4/kotaaaa  [no test files]
+ok      github.com/kotaaaa/gopherdojo-studyroom/kadai4/kotaaaa/fortune  0.007s  coverage: 46.2% of statements
+ok      github.com/kotaaaa/gopherdojo-studyroom/kadai4/kotaaaa/handler  0.013s  coverage: 73.1% of statements
+$ go test ./...  -v
+```
diff --git a/kadai4/kotaaaa/fortune/fortune.go b/kadai4/kotaaaa/fortune/fortune.go
new file mode 100644
index 00000000..28f080fe
--- /dev/null
+++ b/kadai4/kotaaaa/fortune/fortune.go
@@ -0,0 +1,46 @@
+package fortune
+
+import (
+	"math/rand"
+	"time"
+)
+
+type Luck int
+
+const (
+	Great      Luck = iota // 大吉
+	Middle                 // 中吉
+	Small                  // 小吉
+	Normal                 // 吉
+	Uncertain              // 末吉
+	Curse                  // 凶
+	GreatCurse             // 大凶
+	Kind                   // 種類数
+)
+
+func (c Luck) String() string {
+	switch c {
+	case Great:
+		return "大吉"
+	case Middle:
+		return "中吉"
+	case Small:
+		return "小吉"
+	case Normal:
+		return "吉"
+	case Uncertain:
+		return "末吉"
+	case Curse:
+		return "凶"
+	case GreatCurse:
+		return "大凶"
+	}
+	panic("Unknown value")
+}
+
+func Draw(t time.Time) Luck {
+	if t.Month() == time.January && t.Day() >= 1 && t.Day() <= 3 {
+		return Great
+	}
+	return Luck(rand.Intn(int(Kind)))
+}
diff --git a/kadai4/kotaaaa/fortune/fortune_test.go b/kadai4/kotaaaa/fortune/fortune_test.go
new file mode 100644
index 00000000..683b8ec3
--- /dev/null
+++ b/kadai4/kotaaaa/fortune/fortune_test.go
@@ -0,0 +1,29 @@
+package fortune
+
+import (
+	"testing"
+	"time"
+)
+
+func TestForecast(t *testing.T) {
+	ti := time.Date(2021, 1, 1, 8, 4, 18, 0, time.UTC)
+	res := Draw(ti)
+	if res.String() != "大吉" {
+		t.Error("Forecast is illigal. Expected 大吉, Result ", res.String())
+	}
+}
+
+func TestForecastNormal(t *testing.T) {
+	ti := time.Date(2021, 1, 1, 8, 4, 18, 0, time.UTC)
+	res := Draw(ti)
+	if res >= 7 {
+		t.Error("Forecast is illigal. Expected <= 7, Result ", res)
+	}
+}
+func TestString(t *testing.T) {
+	c := Luck(2)
+	res := c.String()
+	if res != "小吉" {
+		t.Error("Forecast is illigal. Expected 中吉, Result ", res)
+	}
+}
diff --git a/kadai4/kotaaaa/handler/handler.go b/kadai4/kotaaaa/handler/handler.go
new file mode 100644
index 00000000..ec211773
--- /dev/null
+++ b/kadai4/kotaaaa/handler/handler.go
@@ -0,0 +1,61 @@
+package handler
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/kotaaaa/gopherdojo-studyroom/kadai4/kotaaaa/fortune"
+)
+
+// API response model
+type ResModel struct {
+	Status string `json:"status"`
+	Result string `json:"result"`
+}
+
+func httpHandler(w http.ResponseWriter, r *http.Request) {
+	p := &ResModel{Status: "", Result: ""}
+	var t time.Time
+	var err error
+	date := r.FormValue("p")
+	timeFormat := "2006-01-02"
+
+	// If request parameter exists
+	fmt.Println("date:", date)
+	if date != "" {
+		t, err = time.Parse(timeFormat, date)
+		if err != nil {
+			fmt.Println(fmt.Errorf("Time format invalid: %v", err.Error()))
+			// w.WriteHeader(http.StatusBadRequest)
+		}
+	} else {
+		t = time.Now()
+	}
+
+	res := fortune.Draw(t)
+	p.Status = "Success"
+	p.Result = res.String()
+	var buf bytes.Buffer
+	err = json.NewEncoder(w).Encode(p)
+	if err != nil {
+		log.Fatal(err)
+	}
+	err = json.NewEncoder(&buf).Encode(p)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(buf.String())
+}
+
+//Run application
+func Run() {
+	http.HandleFunc("/draw", httpHandler)
+	err := http.ListenAndServe(":8080", nil)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
diff --git a/kadai4/kotaaaa/handler/handler_test.go b/kadai4/kotaaaa/handler/handler_test.go
new file mode 100644
index 00000000..2f6b8642
--- /dev/null
+++ b/kadai4/kotaaaa/handler/handler_test.go
@@ -0,0 +1,48 @@
+package handler
+
+import (
+	"encoding/json"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestHandler(t *testing.T) {
+	cases := []struct {
+		name           string
+		date           string
+		expectedResult bool
+		expected       string
+		statusCode     int
+	}{
+		{name: "No date", date: "", statusCode: 200},
+		{name: "12/31", date: "2020-12-31", statusCode: 200},
+		{name: "New Year's Day", date: "2021-01-01", expectedResult: true, expected: "大吉", statusCode: 200},
+		{name: "1/2", date: "2021-01-02", expectedResult: true, expected: "大吉", statusCode: 200},
+		{name: "1/3", date: "2021-01-03", expectedResult: true, expected: "大吉", statusCode: 200},
+		{name: "3/9", date: "2021-03-09", statusCode: 200},
+		{name: "Not found a]", date: "2021-03-09", statusCode: 200},
+	}
+
+	for _, c := range cases {
+		c := c
+		t.Run(c.name, func(t *testing.T) {
+			w := httptest.NewRecorder()
+			r := httptest.NewRequest("GET", "/draw?p="+c.date, nil)
+			httpHandler(w, r)
+			rw := w.Result()
+			defer rw.Body.Close()
+			if rw.StatusCode != c.statusCode {
+				t.Fatal("Unexpected status code")
+			}
+
+			var res ResModel
+			dec := json.NewDecoder(rw.Body)
+			if err := dec.Decode(&res); err != nil {
+				t.Fatal(err)
+			}
+			if c.expectedResult && c.expected != res.Result {
+				t.Errorf("Result is illigal. Expected %v, Result %v", c.expected, res.Result)
+			}
+		})
+	}
+}
diff --git a/kadai4/kotaaaa/main.go b/kadai4/kotaaaa/main.go
new file mode 100644
index 00000000..9bce5ae5
--- /dev/null
+++ b/kadai4/kotaaaa/main.go
@@ -0,0 +1,16 @@
+package main
+
+import (
+	"math/rand"
+	"time"
+
+	"github.com/kotaaaa/gopherdojo-studyroom/kadai4/kotaaaa/handler"
+)
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
+func main() {
+	handler.Run()
+}