A control valve (40) is provided to be mainly used in a clutch-less compressor of the type in which displacement of the compressor is varied depending on the inclination of a drive plate (17) which varies depending on the crank pressure. The control valve (40) includes biasing means (47,52) that applies force to a valve body (46), a force transferring member (65) that urges the valve body (46) to forcibly open the valve against the force of the biasing means (47,52) and the pressure difference between a crank chamber (3) and a suction chamber (8) of the compressor, and a solenoid assembly (60) to actuate the force transferring member (65). The valve remains closed when no electric current is supplied to the solenoid assembly (60), regardless of the crank pressure or the suction pressure. This facilitates minimum displacement operation of the compressor for a desired period of time and therefore makes the valve suitable for a clutch-less type compressor that is directly connected to an engine with a belt and/or a pulley.