PURPOSE: To improve the efficiency of a compressor by constructing a check valve for allowing flow-out through a delivery port to a delivery path with two check valves having different setting levels of differential pressure.

CONSTITUTION: A check valve 21 for allowing flow-out through a delivery port 18 to a delivery path 20 is constructed with first and second check valves 22, 23. The spring force of a first spring member 71 is determined according to a primary setting pressure while the spring force of a second spring member 74 is determined according to a secondary setting pressure. Consequently, the first check valve 22 is suitable for small flow where the residual volume can be reduced by the small path of the check valve 22 thereby the efficiency of compressor can be improved.