Class not found

我的控制器Controller

use APP\Bulletin;
public function store(Request $request)
    {
       $bool=Bulletin::create($request->all());
       return back();
    }

我的模型MODEL

class Bulletin extends Model
{
    //
    protected $table = 'bulletin'; //指定表名
    protected $primarykey = 'id'; //指定KEY

    public $timestamps = true;

    protected $fillable = [
    'bulletin_title','bulletin_content','bulletin_date','bulletin_public','bulletin_type','bulletin_business','bulletin_response'
    ];
}

不知道為什麼會一直報 Class 'APP\Bulletin' not found