A piston compressor includes a rotary valve (35) having a suction guide hole. A plurality of introducing passages are formed in a cylinder block to connect compression chambers to the rotary valve (35). The inner circumferential surface of each cylinder bore has a suction auxiliary recess (61), which is connected to the outlet of the corresponding introducing passage in the circumferential direction of the cylinder bore at the end of the cylinder bore facing a valve assembly. Therefore, the compressor reduces suction resistance of gas at the beginning of the suction stroke without enlarging introducing passages formed in the cylinder block.