diff --git a/kadai4/nguyengiabk/.gitignore b/kadai4/nguyengiabk/.gitignore
new file mode 100644
index 0000000..b1174a0
--- /dev/null
+++ b/kadai4/nguyengiabk/.gitignore
@@ -0,0 +1 @@
+kadai4
diff --git a/kadai4/nguyengiabk/README.md b/kadai4/nguyengiabk/README.md
new file mode 100644
index 0000000..16fcc2d
--- /dev/null
+++ b/kadai4/nguyengiabk/README.md
@@ -0,0 +1,25 @@
+# Gopher Dojo 3 - Kadai4
+## Problem
+
+おみくじAPIを作ってみよう
+* [x] JSON形式でおみくじの結果を返す
+* [x] 正月（1/1-1/3）だけ大吉にする
+* [x] ハンドラのテストを書いてみる
+
+## Build
+```
+$ go build -o kadai4 .
+```
+
+## Usage
+
+Start server
+```
+$ ./kadai4
+```
+
+Client send request
+```
+$ curl localhost:8080
+{"result":"凶"}
+```
diff --git a/kadai4/nguyengiabk/main.go b/kadai4/nguyengiabk/main.go
new file mode 100644
index 0000000..7d4bd0e
--- /dev/null
+++ b/kadai4/nguyengiabk/main.go
@@ -0,0 +1,61 @@
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+
+	"github.com/gopherdojo/dojo3/kadai4/nguyengiabk/omikuji"
+)
+
+// Result represents api response structure
+type Result struct {
+	Result omikuji.Fortune `json:"result"`
+}
+
+// JSONEncoder is used to encode JSON
+type JSONEncoder interface {
+	Encode(interface{}, io.Writer) error
+}
+
+// JSONEncodeFunc is function that used to encode JSON
+type JSONEncodeFunc func(interface{}, io.Writer) error
+
+// Encode encode JSON and write result to writer
+func (f JSONEncodeFunc) Encode(data interface{}, w io.Writer) error {
+	return f(data, w)
+}
+
+// OmikujiServer handles request and response as JSON
+type OmikujiServer struct {
+	jsonEncoder JSONEncoder
+	omikuji     omikuji.Omikuji
+}
+
+func (os *OmikujiServer) encode(data interface{}, w io.Writer) error {
+	if os.jsonEncoder != nil {
+		return os.jsonEncoder.Encode(data, w)
+	}
+	encoder := json.NewEncoder(w)
+	if err := encoder.Encode(data); err != nil {
+		return err
+	}
+	return nil
+}
+
+// ServerErrorMessage is message that will be returned to user in case of error
+const serverErrorMessage = "Server error"
+
+func (os *OmikujiServer) handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	res := Result{os.omikuji.GetResult()}
+	if err := os.encode(res, w); err != nil {
+		http.Error(w, serverErrorMessage, http.StatusInternalServerError)
+	}
+}
+
+func main() {
+	os := OmikujiServer{omikuji: omikuji.Omikuji{}}
+	http.HandleFunc("/", os.handler)
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/kadai4/nguyengiabk/main_test.go b/kadai4/nguyengiabk/main_test.go
new file mode 100644
index 0000000..51fc6e3
--- /dev/null
+++ b/kadai4/nguyengiabk/main_test.go
@@ -0,0 +1,71 @@
+package main
+
+import (
+	"errors"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gopherdojo/dojo3/kadai4/nguyengiabk/omikuji"
+)
+
+type testCase struct {
+	os         OmikujiServer
+	statusCode int
+	response   string
+}
+
+var TestHandlerFixtures = map[string]testCase{
+	"Test json encode error": {
+		OmikujiServer{
+			JSONEncodeFunc(func(data interface{}, w io.Writer) error {
+				return errors.New("Encode error")
+			}),
+			omikuji.Omikuji{},
+		},
+		http.StatusInternalServerError,
+		"Server error\n",
+	},
+	"Test normal case": {
+		OmikujiServer{
+			// want to fixed response
+			omikuji: omikuji.Omikuji{Randomize: omikuji.RandomizeFunc(func(max int) int {
+				return 0
+			})},
+		},
+		http.StatusOK,
+		"{\"result\":\"大吉\"}\n",
+	},
+}
+
+func TestHandler(t *testing.T) {
+	for name, tc := range TestHandlerFixtures {
+		tc := tc
+		t.Run(name, func(t *testing.T) {
+			RunTestCase(t, tc)
+		})
+	}
+}
+
+// split to use defer
+func RunTestCase(t *testing.T, tc testCase) {
+	t.Helper()
+	w := httptest.NewRecorder()
+	r := httptest.NewRequest("GET", "/", nil)
+	tc.os.handler(w, r)
+	rw := w.Result()
+	defer rw.Body.Close()
+
+	if rw.StatusCode != tc.statusCode {
+		t.Errorf("unexpected status code, actual = %v, expected = %v", rw.StatusCode, tc.statusCode)
+	}
+	b, err := ioutil.ReadAll(rw.Body)
+	if err != nil {
+		t.Errorf("unexpected error when read response body")
+	}
+	if s := string(b); s != tc.response {
+		t.Fatalf("unexpected response: actual = %s, expected = %s", s, tc.response)
+	}
+}
diff --git a/kadai4/nguyengiabk/omikuji/omikuji.go b/kadai4/nguyengiabk/omikuji/omikuji.go
new file mode 100644
index 0000000..ee04e45
--- /dev/null
+++ b/kadai4/nguyengiabk/omikuji/omikuji.go
@@ -0,0 +1,92 @@
+package omikuji
+
+import (
+	"math/rand"
+	"time"
+)
+
+// Fortune represents omikuji result
+type Fortune string
+
+const (
+	// Daikichi represents 大吉 result
+	Daikichi Fortune = "大吉"
+
+	// Chukichi represents 中吉 result
+	Chukichi Fortune = "中吉"
+
+	// Shokichi represents 小吉 result
+	Shokichi Fortune = "小吉"
+
+	// Kichi represents 吉 result
+	Kichi Fortune = "吉"
+
+	// Kyou represents 凶 result
+	Kyou Fortune = "凶"
+
+	// Shokyou represents 小凶 result
+	Shokyou Fortune = "小凶"
+
+	// Daikyou represents 大凶 result
+	Daikyou Fortune = "大凶"
+)
+
+var omikujiValues = []Fortune{Daikichi, Chukichi, Shokichi, Kichi, Kyou, Shokyou, Daikyou}
+
+// Clock defines types that can return current time
+type Clock interface {
+	Now() time.Time
+}
+
+// ClockFunc returns current time, we use this type for testing
+type ClockFunc func() time.Time
+
+// Now returns current time by calling CockFunc itself
+func (f ClockFunc) Now() time.Time {
+	return f()
+}
+
+// Randomize defines types that can return ramdom integer
+type Randomize interface {
+	Rand(max int) int
+}
+
+// RandomizeFunc returns randome integer, we use this type for testing
+type RandomizeFunc func(max int) int
+
+// Rand returns random integer by calling RandomizeFunc itself
+func (f RandomizeFunc) Rand(max int) int {
+	return f(max)
+}
+
+// Omikuji is used to get omikuji result based on current time
+type Omikuji struct {
+	Clock     Clock
+	Randomize Randomize
+}
+
+func (o *Omikuji) now() time.Time {
+	if o.Clock == nil {
+		return time.Now()
+	}
+	return o.Clock.Now()
+}
+
+func (o *Omikuji) rand(max int) int {
+	if o.Randomize == nil {
+		rand.Seed(time.Now().UnixNano())
+		return rand.Intn(max)
+	}
+	return o.Randomize.Rand(max)
+}
+
+// GetResult return randomly selected omikuji value
+func (o *Omikuji) GetResult() Fortune {
+	_, m, d := o.now().Date()
+	switch {
+	case m == time.January && d <= 3:
+		return Daikichi
+	default:
+		return omikujiValues[o.rand(len(omikujiValues))]
+	}
+}
diff --git a/kadai4/nguyengiabk/omikuji/omikuji_test.go b/kadai4/nguyengiabk/omikuji/omikuji_test.go
new file mode 100644
index 0000000..b4c1f88
--- /dev/null
+++ b/kadai4/nguyengiabk/omikuji/omikuji_test.go
@@ -0,0 +1,72 @@
+package omikuji_test
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/gopherdojo/dojo3/kadai4/nguyengiabk/omikuji"
+)
+
+func Example() {
+	o := omikuji.Omikuji{}
+	fmt.Println(o.GetResult())
+}
+
+type randomize struct {
+	useMock    bool
+	randResult int
+}
+
+var testGetResultFixtures = map[string]struct {
+	date      string
+	randomize randomize
+	result    omikuji.Fortune
+}{
+	"Test 1/1":                   {"2018/01/01", randomize{false, 0}, omikuji.Daikichi},
+	"Test 1/2":                   {"2018/01/02", randomize{false, 0}, omikuji.Daikichi},
+	"Test 1/3":                   {"2018/01/03", randomize{false, 0}, omikuji.Daikichi},
+	"Test 1/4 and Kyou":          {"2018/01/04", randomize{true, 4}, omikuji.Kyou},
+	"Test Daikichi not new year": {"2018/07/01", randomize{true, 0}, omikuji.Daikichi},
+	"Test Chukichi":              {"2018/08/02", randomize{true, 1}, omikuji.Chukichi},
+	"Test Shokichi":              {"2018/09/10", randomize{true, 2}, omikuji.Shokichi},
+	"Test Shokyou":               {"2018/10/11", randomize{true, 5}, omikuji.Shokyou},
+	"Test Daikyou":               {"2018/03/21", randomize{true, 6}, omikuji.Daikyou},
+}
+
+func TestGetResult(t *testing.T) {
+	for name, tc := range testGetResultFixtures {
+		tc := tc
+		t.Run(name, func(t *testing.T) {
+			clock := mockClock(t, tc.date)
+			var randomize omikuji.Randomize
+			if tc.randomize.useMock {
+				randomize = mockRandomize(t, tc.randomize.randResult)
+			}
+			o := omikuji.Omikuji{Clock: clock, Randomize: randomize}
+			result := o.GetResult()
+			if result != tc.result {
+				t.Errorf("GetResult() return wrong result, actual = %v, expected = %v", result, tc.result)
+			}
+		})
+	}
+}
+
+func mockClock(t *testing.T, v string) omikuji.Clock {
+	t.Helper()
+	now, err := time.Parse("2006/01/02", v)
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	return omikuji.ClockFunc(func() time.Time {
+		return now
+	})
+}
+
+func mockRandomize(t *testing.T, v int) omikuji.Randomize {
+	t.Helper()
+	return omikuji.RandomizeFunc(func(max int) int {
+		return v
+	})
+}