A piston type compressor having a cylinder block in which a plurality of compression chambers permit a plurality of pistons to be reciprocated so as to compress a refrigerant gas pumped from a suction chamber formed in an end housing into the compression chambers through suction ports of a valve plate, openably closed by a suction valve mechanism with a plurality of suction reed valves oscillatorily movable with regard to two bearing points, respectively, and to discharge the compressed refrigerant gas from the compression chambers into a discharge chamber formed in the end housing through discharge ports of the valve plate, openably closed by a discharge valve mechanism having a plurality of discharge reed valves oscillatorily movable with regard to two bearing points, respectively. The suction and discharge reed valves of the suction and discharge valve mechanisms are prevented suffering the effect of complicated and irregular vibrations by an asymmetrical arrangement of the suction and discharge ports of the valve plate with regard to bisectors perpendicular to lines connecting the respective two bearing points.