diff --git a/error.go b/error.go
index 45f89f1..ffa7ebd 100644
--- a/error.go
+++ b/error.go
@@ -30,6 +30,9 @@ const (
 	// ErequiredType means the type mismatch against user required one.
 	// For example M() requires map, A() requires array.
 	ErequiredType
+
+	// EinvalidValue means proxy can't treat the value.
+	EinvalidValue
 )
 
 func (et ErrorType) String() string {
@@ -48,6 +51,8 @@ func (et ErrorType) String() string {
 		return "EinvalidQuery"
 	case ErequiredType:
 		return "ErequiredType"
+	case EinvalidValue:
+		return "EinvalidValue"
 	default:
 		return "Eunknown"
 	}
@@ -205,6 +210,9 @@ func (p *errorProxy) Error() string {
 	case ErequiredType:
 		return fmt.Sprintf("not required types: required=%s actual=%s: %s",
 			p.expected.String(), p.actual.String(), p.FullAddress())
+	case EinvalidValue:
+		// FIXME: better error message.
+		return fmt.Sprintf("invalid value: %s: %s", p.infoStr, p.FullAddress())
 	default:
 		return fmt.Sprintf("unexpected: %s", p.FullAddress())
 	}
diff --git a/go.mod b/go.mod
index d34f7be..358c38d 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module github.com/koron/go-dproxy
 
-go 1.13
+go 1.21
+
+require github.com/google/go-cmp v0.7.0
diff --git a/go.sum b/go.sum
index e69de29..40e761a 100644
--- a/go.sum
+++ b/go.sum
@@ -0,0 +1,2 @@
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
diff --git a/package_test.go b/package_test.go
index 88ba1f7..59fa462 100644
--- a/package_test.go
+++ b/package_test.go
@@ -1,16 +1,15 @@
 package dproxy
 
 import (
-	"fmt"
-	"reflect"
 	"testing"
+
+	"github.com/google/go-cmp/cmp"
 )
 
-func assertEquals(t *testing.T, actual, expected interface{}, format string, a ...interface{}) {
+func assertEquals(t *testing.T, want, got any) {
 	t.Helper()
-	if !reflect.DeepEqual(actual, expected) {
-		msg := fmt.Sprintf(format, a...)
-		t.Errorf("not equal: %s\nexpect=%+v\nactual=%+v", msg, expected, actual)
+	if d := cmp.Diff(want, got); d != "" {
+		t.Errorf("not equal -want +got\n%s", d)
 	}
 }
 
diff --git a/pointer_test.go b/pointer_test.go
index db0069e..87a0739 100644
--- a/pointer_test.go
+++ b/pointer_test.go
@@ -33,13 +33,14 @@ func TestPointerInvalidQuery(t *testing.T) {
 
 func TestPointer(t *testing.T) {
 	f := func(q string, d, expected interface{}) {
+		t.Helper()
 		p := Pointer(d, q)
 		v, err := p.Value()
 		if err != nil {
 			t.Errorf("Pointer:%q for %+v failed: %s", q, d, err)
 			return
 		}
-		assertEquals(t, v, expected, "Pointer:%q for %+v", q, d)
+		assertEquals(t, expected, v)
 	}
 
 	v := parseJSON(`{
diff --git a/reflect.go b/reflect.go
new file mode 100644
index 0000000..820f571
--- /dev/null
+++ b/reflect.go
@@ -0,0 +1,211 @@
+package dproxy
+
+import (
+	"fmt"
+	"reflect"
+	"strconv"
+)
+
+// reflectProxy is a proxy using reflect.
+type reflectProxy struct {
+	rv reflect.Value
+	p  frame  // parent
+	l  string // label
+}
+
+var _ Proxy = (*reflectProxy)(nil)
+
+// NewReflect creates a new proxy with reflect.
+func NewReflect(v interface{}) Proxy {
+	return newReflectProxy(v, nil, "")
+}
+
+func newReflectProxy(v interface{}, parent frame, label string) Proxy {
+	rv := reflect.ValueOf(v)
+	for rv.Kind() == reflect.Ptr {
+		rv = rv.Elem()
+		if !rv.IsValid() {
+			return &errorProxy{
+				errorType: EinvalidValue,
+				parent:    parent,
+				label:     label,
+				infoStr:   fmt.Sprintf("%T", v),
+			}
+		}
+	}
+	return &reflectProxy{rv: rv, p: parent, l: label}
+}
+
+func (rp *reflectProxy) parentFrame() frame {
+	return rp.p
+}
+
+func (rp *reflectProxy) frameLabel() string {
+	return rp.l
+}
+
+func (rp *reflectProxy) typeError(expected Type) *errorProxy {
+	return typeError(rp, expected, rp.rv.Interface())
+}
+
+func (rp *reflectProxy) Nil() bool {
+	return !rp.rv.IsValid()
+}
+
+func (rp *reflectProxy) Value() (interface{}, error) {
+	return rp.rv.Interface(), nil
+}
+
+func (rp *reflectProxy) Bool() (bool, error) {
+	switch rp.rv.Kind() {
+	case reflect.Bool:
+		return rp.rv.Bool(), nil
+	default:
+		return false, rp.typeError(Tbool)
+	}
+}
+
+func (rp *reflectProxy) isInt() bool {
+	switch rp.rv.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return true
+	default:
+		return false
+	}
+}
+
+func (rp *reflectProxy) Int64() (int64, error) {
+	if !rp.isInt() {
+		return 0, rp.typeError(Tint64)
+	}
+	return rp.rv.Int(), nil
+}
+
+func (rp *reflectProxy) isFloat() bool {
+	switch rp.rv.Kind() {
+	case reflect.Float32, reflect.Float64:
+		return true
+	default:
+		return false
+	}
+}
+
+func (rp *reflectProxy) Float64() (float64, error) {
+	if !rp.isFloat() {
+		return 0, rp.typeError(Tfloat64)
+	}
+	return rp.rv.Float(), nil
+}
+
+func (rp *reflectProxy) String() (string, error) {
+	if rp.rv.Kind() != reflect.String {
+		return "", rp.typeError(Tstring)
+	}
+	return rp.rv.String(), nil
+}
+
+func (rp *reflectProxy) Array() ([]interface{}, error) {
+	if !rp.isArray() {
+		return nil, rp.typeError(Tarray)
+	}
+	if v, ok := rp.rv.Interface().([]interface{}); ok {
+		return v, nil
+	}
+	v := make([]interface{}, rp.rv.Len())
+	for i := range v {
+		v[i] = rp.rv.Index(i).Interface()
+	}
+	return v, nil
+}
+
+func (rp *reflectProxy) Map() (map[string]interface{}, error) {
+	if rp.rv.Kind() != reflect.Map {
+		return nil, rp.typeError(Tmap)
+	}
+	if v, ok := rp.rv.Interface().(map[string]interface{}); ok {
+		return v, nil
+	}
+	v := map[string]interface{}{}
+	for _, k := range rp.rv.MapKeys() {
+		v[k.String()] = rp.rv.MapIndex(k)
+	}
+	return v, nil
+}
+
+func (rp *reflectProxy) isArray() bool {
+	switch rp.rv.Kind() {
+	case reflect.Array, reflect.Slice:
+		return true
+	default:
+		return false
+	}
+}
+
+func (rp *reflectProxy) A(n int) Proxy {
+	if !rp.isArray() {
+		return rp.typeError(Tarray)
+	}
+	adrs := "[" + strconv.Itoa(n) + "]"
+	if n < 0 || n >= rp.rv.Len() {
+		return notfoundError(rp, adrs)
+	}
+	v := rp.rv.Index(n)
+	return newReflectProxy(v.Interface(), rp, adrs)
+}
+
+func (rp *reflectProxy) M(k string) Proxy {
+	adrs := "." + k
+	switch rp.rv.Kind() {
+	case reflect.Map:
+		v := rp.rv.MapIndex(reflect.ValueOf(k))
+		if !v.IsValid() {
+			return notfoundError(rp, adrs)
+		}
+		return newReflectProxy(v.Interface(), rp, adrs)
+	case reflect.Struct:
+		v := rp.rv.FieldByName(k)
+		if !v.IsValid() {
+			return notfoundError(rp, adrs)
+		}
+		return newReflectProxy(v.Interface(), rp, adrs)
+	default:
+		return rp.typeError(Tmap)
+	}
+}
+
+func (rp *reflectProxy) P(q string) Proxy {
+	return pointer(rp, q)
+}
+
+func (rp *reflectProxy) ProxySet() ProxySet {
+	// TODO: return proxy set for reflect vaue.
+	return nil
+}
+
+func (rp *reflectProxy) Q(k string) ProxySet {
+	// TODO: return proxy set for queried value
+	return nil
+}
+
+func (rp *reflectProxy) findJPT(t string) Proxy {
+	switch rp.rv.Kind() {
+	case reflect.Map, reflect.Struct:
+		return rp.M(t)
+	case reflect.Array, reflect.Slice:
+		n, err := strconv.ParseUint(t, 10, 0)
+		if err != nil {
+			return &errorProxy{
+				errorType: EinvalidIndex,
+				parent:    rp,
+				infoStr:   err.Error(),
+			}
+		}
+		return rp.A(int(n))
+	default:
+		return &errorProxy{
+			errorType: EmapNorArray,
+			parent:    rp,
+			actual:    detectType(rp.rv.Interface()),
+		}
+	}
+}
diff --git a/reflect_test.go b/reflect_test.go
new file mode 100644
index 0000000..d7b5830
--- /dev/null
+++ b/reflect_test.go
@@ -0,0 +1,90 @@
+package dproxy
+
+import "testing"
+
+func TestReflect_Readme(t *testing.T) {
+	v := parseJSON(`{
+		"cities": [ "tokyo", 100, "osaka", 200, "hakata", 300 ],
+		"data": {
+			"custom": [ "male", 21, "female", 22 ]
+		}
+	}`)
+
+	s, err := NewReflect(v).M("cities").A(0).String()
+	if s != "tokyo" {
+		t.Error("cities[0] must be \"tokyo\":", err)
+	}
+
+	_, err = NewReflect(v).M("cities").A(0).Float64()
+	if err == nil {
+		t.Error("cities[0] (float64) must be failed:", err)
+	}
+
+	n, err := NewReflect(v).M("cities").A(1).Float64()
+	if n != 100 {
+		t.Error("cities[1] must be 100:", err)
+	}
+
+	s2, err := NewReflect(v).M("data").M("custom").A(2).String()
+	if s2 != "female" {
+		t.Error("data.custom[2] must be \"female\":", err)
+	}
+
+	_, err = NewReflect(v).M("data").M("kustom").String()
+	if err == nil || err.Error() != "not found: data.kustom" {
+		t.Error("err is not \"not found: data.kustom\":", err)
+	}
+}
+
+func TestReflect_MapBool(t *testing.T) {
+	v := parseJSON(`{
+		"foo": true,
+		"bar": false
+	}`)
+
+	// check "foo"
+	foo, err := NewReflect(v).M("foo").Bool()
+	if err != nil {
+		t.Error(err)
+	} else if foo != true {
+		t.Errorf("foo must be true")
+	}
+
+	// check "bar"
+	bar, err := NewReflect(v).M("bar").Bool()
+	if err != nil {
+		t.Error(err)
+	} else if bar != false {
+		t.Errorf("bar must be false")
+	}
+}
+
+func TestReflectMisc(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		if NewReflect(nil).Nil() == false {
+			t.Error("nil.Nil() should true but false")
+		}
+		if NewReflect("foo").Nil() == true {
+			t.Error("string.Nil() should false but true")
+		}
+	})
+}
+
+func TestReflect_Array(t *testing.T) {
+	got1, err := NewReflect(parseJSON(`{
+		"cities": [ "tokyo", 100, "osaka", 200, "hakata", 300 ]
+	}`)).M("cities").Array()
+	if err != nil {
+		t.Fatalf("not array: %s", err)
+	}
+	assertEquals(t, []any{"tokyo", 100.0, "osaka", 200.0, "hakata", 300.0}, got1)
+
+	got2, err := NewReflect([]string{"foo", "bar", "baz"}).Array()
+	if err != nil {
+		t.Fatalf("not array: %s", err)
+	}
+	assertEquals(t, []any{"foo", "bar", "baz"}, got2)
+
+	_, err = NewReflect(0).Array()
+	assertError(t, err, "not matched types: expected=array actual=int64: (root)")
+}