A compressor has a drive plate located in a crank chamber and tiltably mounted on a drive shaft and a piston operably coupled to the drive plate and located in a cylinder bore. The inclination of the drive plate is variable according to a difference between the pressure in the crank chamber and the pressure in the cylinder bore. The compressor has an adjusting mechanism for adjusting the pressure in one of the crank chamber and a suction chamber to vary the difference between the pressure in the crank chamber and the pressure in the cylinder bore. The adjusting mechanism includes a gas passage for passing the gas used for adjusting the pressure and a control valve for adjusting the amount of the gas flowing in the gas passage. The control valve includes a valve body, a reacting member and a solenoid. The valve body adjusts the opening size of the gas passage. The reacting member moves the valve body in accordance with the pressure of the gas supplied to the compressor from the external circuit. The solenoid biases the valve body in a direction with the force based on a value of current supplied to the solenoid. A supplying apparatus supplies undulating current to the solenoid. The supplying apparatus varies the average value of the undulating current to vary the biasing force of the solenoid.