A piston compressor having cylinder blocks, each defining cylinder bores in which a piston is axially reciprocally arranged. Front and rear housings are connected to the cylinder blocks via valve port plates, so that compression chambers are formed between the valve port plates and the cylinder blocks and inlet and outlet chambers are formed between the valve port plates. The valve port plates form inlet and outlet ports for each of the compression chambers and inlet valves and outlet valves formed as thin resilient web members are provided for the inlet and outlet ports, respectively, to control the feeding and discharge of the gas, respectively. The valve port plates having, on the surfaces thereof facing the outlet valve around the inlet ports, a roughened area having a surface roughness value R.sub.z of between 10 to 25 .mu.m and an average spacing value L of between to 50 to 100 .mu.m.