Refrigerant gas is introduced into a suction chamber through a suction line. Refrigerant gas is allowed to flow from the crank chamber into the suction chamber through an outlet line. An open degree adjustment valve (34) has a first valve body for adjusting an open degree of the suction line and a second valve body for adjusting an open degree of the outlet line. The first valve body and the second valve body are connected to each other. The first valve body moves in such a manner as to increase the open degree of the suction line when the difference between the pressure in the suction chamber and the pressure in the crank chamber decreases, and reduce the open degree of the suction line when the difference between the pressure in the suction chamber and the pressure in the crank chamber increases. Thus, variation of gas pressure is reliably suppressed while maintaining favorable starting performance of the compressor.