The present invention provides a piston compressor capable of changing the flow rate of a refrigerant discharged from a compressor to an external refrigerant circuit of the compressor, and capable ofreducing power loss, vibration, and torque fluctuation in a low flow rate state while simplifying the structure. In this piston compressor, a rotating body integrated with or separated from a drive shaft (3) can rotate integrally with the drive shaft (3), and a second communication path (45a) or the like that intermittently communicates with first communication paths (41Fa-41Fe) or the like in accordance with the rotation of the drive shaft (3) is formed. A suction valve (9F) or the like sucks a refrigerant in a suction chamber (21a) or the like into the compression chamber (51F) or the like.A control valve (13) controls the flow rate at which the refrigerant in the discharge chamber (23b) returns to the compression chamber (51F) or the like. The refrigerant controlled by the control valve (13) is introduced into the compression chamber (51F) or the like via the first communication paths (41Fa-41Fe) or the like and the second communication path (45a) or the like, and the flow rate ofthe refrigerant discharged from the compressor to an external refrigerant circuit of the compressor is changed.