diff --git a/app/Http/Requests/V1/Bill/StoreBillRequest.php b/app/Http/Requests/V1/Bill/StoreBillRequest.php
index 01c262e..562dc98 100644
--- a/app/Http/Requests/V1/Bill/StoreBillRequest.php
+++ b/app/Http/Requests/V1/Bill/StoreBillRequest.php
@@ -3,6 +3,7 @@
 namespace App\Http\Requests\V1\Bill;
 
 use Illuminate\Foundation\Http\FormRequest;
+use Illuminate\Validation\Rule;
 
 class StoreBillRequest extends FormRequest
 {
@@ -13,8 +14,17 @@ public function authorize(): bool
 
     public function rules(): array
     {
+        $tenantId = app('tenant_id') ?? 0;
+
         return [
-            'bill_number' => ['nullable', 'string', 'max:50'],
+            'bill_number' => [
+                'nullable',
+                'string',
+                'max:50',
+                Rule::unique('bills', 'bill_number')->where(function ($query) use ($tenantId) {
+                    return $query->where('tenant_id', $tenantId);
+                }),
+            ],
             'bill_type' => ['required', 'string', 'in:received,issued'],
             'client_id' => ['nullable', 'integer', 'exists:clients,id'],
             'client_name' => ['nullable', 'string', 'max:100'],
@@ -37,6 +47,7 @@ public function rules(): array
     public function messages(): array
     {
         return [
+            'bill_number.unique' => __('error.bill.duplicate_number'),
             'bill_type.required' => __('validation.required', ['attribute' => __('validation.attributes.bill_type')]),
             'bill_type.in' => __('validation.in', ['attribute' => __('validation.attributes.bill_type')]),
             'amount.required' => __('validation.required', ['attribute' => __('validation.attributes.amount')]),
diff --git a/lang/ko/error.php b/lang/ko/error.php
index 7f8fb4e..139f0c9 100644
--- a/lang/ko/error.php
+++ b/lang/ko/error.php
@@ -289,6 +289,11 @@
         'recipient_email_required' => '수신자 이메일이 필요합니다.',
     ],
 
+    // 어음 관리 관련
+    'bill' => [
+        'duplicate_number' => '이미 존재하는 어음번호입니다.',
+    ],
+
     // 계정 관리 관련
     'account' => [
         'invalid_password' => '비밀번호가 일치하지 않습니다.',