diff --git a/internal/console/console.go b/internal/console/console.go
index e1a3b4a..511865e 100644
--- a/internal/console/console.go
+++ b/internal/console/console.go
@@ -39,7 +39,7 @@ func HomeCursor() {
 }
 
 func MoveCursor(x, y int) {
-	fmt.Printf("\x1b[%d;%dH", y + 1, x + 1)
+	fmt.Printf("\x1b[%d;%dH", y+1, x+1)
 }
 
 func HideCursor() {
@@ -60,13 +60,13 @@ func Size() (int, int) {
 
 func runeSize(b byte) int {
 	switch {
-	case b & 0x80 == 0:
+	case b&0x80 == 0:
 		return 1
-	case b & 0xe0 == 0xc0:
+	case b&0xe0 == 0xc0:
 		return 2
-	case b & 0xf0 == 0xe0:
+	case b&0xf0 == 0xe0:
 		return 3
-	case b & 0xf8 == 0xf0:
+	case b&0xf8 == 0xf0:
 		return 4
 	default:
 		return -1 // invalid
diff --git a/internal/editor/editor.go b/internal/editor/editor.go
index 7673807..af2d018 100644
--- a/internal/editor/editor.go
+++ b/internal/editor/editor.go
@@ -2,6 +2,7 @@ package editor
 
 import (
 	"strings"
+	"unicode/utf8"
 
 	"tea.kareha.org/lab/levi/internal/console"
 	"tea.kareha.org/lab/levi/internal/util"
@@ -15,11 +16,13 @@ const (
 )
 
 type Editor struct {
-	scr *Screen
-	kb *Keyboard
-	x, y int
-	line *strings.Builder
-	mode mode
+	scr        *Screen
+	kb         *Keyboard
+	col, row   int
+	x, y       int
+	head, tail string
+	insert     *strings.Builder
+	mode       mode
 }
 
 func New() *Editor {
@@ -27,33 +30,54 @@ func New() *Editor {
 	kb := NewKeyboard()
 
 	return &Editor{
-		scr: &scr,
-		kb: &kb,
-		x: 0,
-		y: 0,
-		line: new(strings.Builder),
-		mode: modeCommand,
+		scr:    &scr,
+		kb:     &kb,
+		col:    0,
+		row:    0,
+		x:      0,
+		y:      0,
+		head:   "",
+		tail:   "",
+		insert: new(strings.Builder),
+		mode:   modeCommand,
 	}
 }
 
 func (ed *Editor) addRune(r rune) {
-	ed.line.WriteRune(r)
+	ed.insert.WriteRune(r)
+}
+
+func (ed *Editor) drawBuffer() {
+	switch ed.mode {
+	case modeCommand:
+		console.Print(ed.head)
+	case modeInsert:
+		console.Print(ed.head)
+		console.Print(ed.insert.String())
+		console.Print(ed.tail)
+	}
 }
 
 func (ed *Editor) drawStatus() {
 	_, h := console.Size()
 
-	console.MoveCursor(0, h - 2)
+	console.MoveCursor(0, h-2)
 	switch ed.mode {
 	case modeCommand:
-		console.Print("-- [command] q: quit, i: insert --")
+		console.Print("-- [command] q: quit, i: insert, a: insert after --")
 	case modeInsert:
 		console.Print("-- [insert] Esc: command mode --")
 	}
 }
 
-func (ed *Editor) drawBuffer() {
-	console.Print(ed.line.String())
+func (ed *Editor) updateCursor() {
+	switch ed.mode {
+	case modeCommand:
+		ed.x = util.StringWidth(ed.head, ed.col)
+	case modeInsert:
+		ed.x = util.StringWidth(ed.head+ed.insert.String(), ed.col)
+	}
+	ed.y = ed.row
 }
 
 func (ed *Editor) repaint() {
@@ -65,11 +89,39 @@ func (ed *Editor) repaint() {
 	ed.drawBuffer()
 	ed.drawStatus()
 
+	ed.updateCursor()
 	console.MoveCursor(ed.x, ed.y)
 
 	console.ShowCursor()
 }
 
+func (ed *Editor) enterInsert() {
+	rs := []rune(ed.head)
+	ed.head = string(rs[:ed.col])
+	ed.tail = string(rs[ed.col:])
+	ed.mode = modeInsert
+}
+
+func (ed *Editor) enterInsertAfter() {
+	len := utf8.RuneCountInString(ed.head)
+	if ed.col < len-1 {
+		ed.moveRight(1)
+		ed.enterInsert()
+		return
+	} else {
+		ed.col++
+		ed.mode = modeInsert
+	}
+}
+
+func (ed *Editor) moveLeft(n int) {
+	ed.col = max(ed.col-n, 0)
+}
+
+func (ed *Editor) moveRight(n int) {
+	ed.col = min(ed.col+n, max(utf8.RuneCountInString(ed.head)-1, 0))
+}
+
 func (ed *Editor) Main() {
 	for {
 		ed.repaint()
@@ -81,15 +133,25 @@ func (ed *Editor) Main() {
 			case 'q':
 				return
 			case 'i':
-				ed.mode = modeInsert
+				ed.enterInsert()
+			case 'a':
+				ed.enterInsertAfter()
+			case 'h':
+				ed.moveLeft(1)
+			case 'l':
+				ed.moveRight(1)
 			}
 		case modeInsert:
 			switch r {
 			case Esc:
+				ed.head = ed.head + ed.insert.String() + ed.tail
+				ed.tail = ""
+				ed.insert = new(strings.Builder)
 				ed.mode = modeCommand
+				ed.moveLeft(1)
 			default:
 				ed.addRune(r)
-				ed.x += util.RuneWidth(r)
+				ed.col++
 			}
 		}
 	}
diff --git a/internal/editor/keyboard.go b/internal/editor/keyboard.go
index 323576c..440878d 100644
--- a/internal/editor/keyboard.go
+++ b/internal/editor/keyboard.go
@@ -6,7 +6,7 @@ import (
 
 const Esc rune = 0x1b
 
-type Keyboard struct {}
+type Keyboard struct{}
 
 func NewKeyboard() Keyboard {
 	return Keyboard{}
diff --git a/internal/util/util.go b/internal/util/util.go
index 97cd773..f7727b6 100644
--- a/internal/util/util.go
+++ b/internal/util/util.go
@@ -5,8 +5,7 @@ import (
 )
 
 func isWide(r rune) bool {
-	return r >= 0x1100 && (
-		r <= 0x115f || // Hangul Jamo
+	return r >= 0x1100 && (r <= 0x115f || // Hangul Jamo
 		r == 0x2329 || r == 0x232a ||
 		(r >= 0x2e80 && r <= 0xa4cf) ||
 		(r >= 0xac00 && r <= 0xd7a3) ||
@@ -47,3 +46,16 @@ func RuneWidth(r rune) int {
 
 	return 1
 }
+
+func StringWidth(s string, col int) int {
+	sum := 0
+	i := 0
+	for _, r := range s {
+		if i >= col {
+			break
+		}
+		sum += RuneWidth(r)
+		i++
+	}
+	return sum
+}