This invention is about a bag for a pet. It has fluid acceptation space which is suitable for physical character of a pet. Also it makes a pet safe and a man easy to walk as wearing more closer to his body. It consist of a main body which of space made bottom gradient to body direction from the front of be in pet's head, a form frame which set a pair with a flexible cushion on open surface and get smaller in diameter, and a changeable length shoulder strap which link both of a main body.