A suction throttle valve of a compressor has a compressor housing having a suction chamber and a crank chamber. The suction throttle valve includes a suction passage formed in the housing, a suction port provided at an inlet of the suction passage, a valve body movably arranged in the suction passage for adjusting opening of the suction passage, an urging member for urging the valve body toward the suction port, and a valve chamber provided in the suction passage. Refrigerant is drawn into the suction passage through the suction port and then received in the suction chamber. A first communication hole is formed through the housing, through which the valve chamber and the suction chamber are in constant communication with each other. A second communication hole is formed through the housing, through which the valve chamber and the crank chamber are in constant communication with each other.