To provide a mattress with advantageous structure with respect to cost without a bed structure, enabling a user to easily change the position of the body variously.

Two circular holes for setting auxiliary materials are formed on a mattress base auxiliary material 4, one in the part to lay a user's legs and the other in the part to lay the user's hips. And a discoidal mattress auxiliary material 5 is detachably and rotatably inserted into each hole for setting auxiliary materials.