To achieve higher accuracy by minimizing hysteresis in valve opening/closing operation even when the straightness of a bellows is somewhat wrong.

There is provided the closed structure bellows 26 as a pressure sensing element. A valve opening amount is changed by transmitting the expansion of the bellows 26 from a valve housing 11 directly to a valve element 21 via an operating ball 25 supported movably in a valve lifting direction. In a control valve 10 being assembled in a variable displacement compressor, when an energizing force of a compression coil spring 30 in a bellows body 27 overcomes suction pressure Ps, a cover member 31 of the expanded bellows body 27 is thrust to the side of an end cap 12. Then, the operating ball 25 thrust by the cover member 31 and an abutting body 31e thrusts the valve element 21 to the side of the end cap 12 against a spring force of the compression coil spring 24 and put it apart from a valve port 16 to make the control valve 10 open.