PURPOSE: To provide a coolant gas suction structure of a piston type compressor that improves the volumetric efficiency of this compressor and also promotes a reduction in power loss.

CONSTITUTION: Six conducting passages 1c to be normally interconnected each to each operating room R in six cylinder bores 1a are opened to an inner circumferential seal surface S2 of a valve storage chamber 22, and an outlet 25a of a suction passage 25 to be opened to an outer circumferential seal surface S1 of a rotary valve 23 is interconnected to the conducting passage 1c in the suction stroke. In addition, this conducting passage is closed by the outer circumferential seal surface S1 of the rotary valve 23 in the discharge stroke. A movable sealing member 26 improving the extent of sealability between the outer circumferential seal surface S1 of the valve closing the conducting passage 1c and the inner circumferential seal surface S2 of the valve storage chamber 22 is installed in the rotary valve 23. In succession, discharge gas in the conducting passage 1c is conducted into a pressure chamber 28 from a passage of the movable sealing member 26, and then this sealing member 26 is pressed to the seal surface S2 under pressure.