diff --git a/src/__tests__/prompt.test.ts b/src/__tests__/prompt.test.ts
index 7c30f06..6095dbe 100644
--- a/src/__tests__/prompt.test.ts
+++ b/src/__tests__/prompt.test.ts
@@ -315,5 +315,30 @@ describe('prompt', () => {
       const result = await selectOptionWithDefault('Test:', [], 'fallback');
       expect(result).toBe('fallback');
     });
+
+    it('should have return type that allows null (cancel)', async () => {
+      const { selectOptionWithDefault } = await import('../prompt/index.js');
+      // When options are empty, default is returned (not null)
+      const result: string | null = await selectOptionWithDefault('Test:', [], 'fallback');
+      expect(result).toBe('fallback');
+    });
+  });
+
+  describe('selectOptionWithDefault cancel behavior', () => {
+    it('handleKeyInput should return cancel with optionCount when hasCancelOption is true', () => {
+      // Simulates ESC key press with cancel option enabled (as selectOptionWithDefault now does)
+      const result = handleKeyInput('\x1B', 0, 4, true, 3);
+      expect(result).toEqual({ action: 'cancel', cancelIndex: 3 });
+    });
+
+    it('handleKeyInput should support navigating to Cancel item', () => {
+      // With 3 options + cancel, totalItems = 4, cancel is at index 3
+      const downResult = handleKeyInput('\x1B[B', 2, 4, true, 3);
+      expect(downResult).toEqual({ action: 'move', newIndex: 3 });
+
+      // Confirming on cancel index (3) should return confirm with selectedIndex 3
+      const confirmResult = handleKeyInput('\r', 3, 4, true, 3);
+      expect(confirmResult).toEqual({ action: 'confirm', selectedIndex: 3 });
+    });
   });
 });
diff --git a/src/cli.ts b/src/cli.ts
index c0d96b4..f9ec44a 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -163,11 +163,18 @@ program
               ? DEFAULT_WORKFLOW_NAME
               : availableWorkflows[0] || DEFAULT_WORKFLOW_NAME);
 
-        selectedWorkflow = await selectOptionWithDefault(
+        const selected = await selectOptionWithDefault(
           'Select workflow:',
           options,
           defaultWorkflow
         );
+
+        if (selected === null) {
+          info('Cancelled');
+          return;
+        }
+
+        selectedWorkflow = selected;
       }
 
       log.info('Starting task execution', { task, workflow: selectedWorkflow });
diff --git a/src/config/initialization.ts b/src/config/initialization.ts
index 146dfdf..132fca6 100644
--- a/src/config/initialization.ts
+++ b/src/config/initialization.ts
@@ -37,6 +37,7 @@ export function needsLanguageSetup(): boolean {
 /**
  * Prompt user to select language for resources.
  * Returns 'en' for English (default), 'ja' for Japanese.
+ * Exits process if cancelled (initial setup is required).
  */
 export async function promptLanguageSelection(): Promise<Language> {
   const options: { label: string; value: Language }[] = [
@@ -44,15 +45,22 @@ export async function promptLanguageSelection(): Promise<Language> {
     { label: '日本語 (Japanese)', value: 'ja' },
   ];
 
-  return await selectOptionWithDefault(
+  const result = await selectOptionWithDefault(
     'Select language for default agents and workflows / デフォルトのエージェントとワークフローの言語を選択してください:',
     options,
     DEFAULT_LANGUAGE
   );
+
+  if (result === null) {
+    process.exit(0);
+  }
+
+  return result;
 }
 
 /**
  * Prompt user to select provider for resources.
+ * Exits process if cancelled (initial setup is required).
  */
 export async function promptProviderSelection(): Promise<'claude' | 'codex'> {
   const options: { label: string; value: 'claude' | 'codex' }[] = [
@@ -60,11 +68,17 @@ export async function promptProviderSelection(): Promise<'claude' | 'codex'> {
     { label: 'Codex', value: 'codex' },
   ];
 
-  return await selectOptionWithDefault(
+  const result = await selectOptionWithDefault(
     'Select provider (Claude Code or Codex) / プロバイダーを選択してください:',
     options,
     'claude'
   );
+
+  if (result === null) {
+    process.exit(0);
+  }
+
+  return result;
 }
 
 /**
diff --git a/src/prompt/index.ts b/src/prompt/index.ts
index 8d507e3..14df192 100644
--- a/src/prompt/index.ts
+++ b/src/prompt/index.ts
@@ -275,13 +275,13 @@ export async function promptInput(message: string): Promise<string | null> {
 /**
  * Prompt user to select from a list of options with a default value.
  * Uses cursor navigation. Enter immediately selects the default.
- * @returns Selected option value
+ * @returns Selected option value, or null if cancelled (ESC pressed)
  */
 export async function selectOptionWithDefault<T extends string>(
   message: string,
   options: { label: string; value: T }[],
   defaultValue: T
-): Promise<T> {
+): Promise<T | null> {
   if (options.length === 0) return defaultValue;
 
   // Find default index
@@ -294,12 +294,11 @@ export async function selectOptionWithDefault<T extends string>(
     label: opt.value === defaultValue ? `${opt.label} ${chalk.green('(default)')}` : opt.label,
   }));
 
-  const selectedIndex = await interactiveSelect(message, decoratedOptions, initialIndex, false);
+  const selectedIndex = await interactiveSelect(message, decoratedOptions, initialIndex, true);
 
-  // Escape pressed - use default
-  if (selectedIndex === -1) {
-    console.log(chalk.gray(`  Using default: ${defaultValue}`));
-    return defaultValue;
+  // Cancel selected (last item) or Escape pressed
+  if (selectedIndex === options.length || selectedIndex === -1) {
+    return null;
   }
 
   const selected = options[selectedIndex];