A displacement control system (B) for a variable displacement compressor has an electromagnetic clutch (200), a displacement control valve (300) including a valve body (306) that is applied with pressure of a suction pressure region of a variable displacement compressor (100) and an electromagnetic force of a solenoid unit in an opposite direction to the pressure of a discharge pressure region, and biasing means that biases the valve body (306) in the same direction as the electromagnetic force, and means (453, 454, 405) for adjusting current, which adjusts current supplied to a displacement control valve coil (316) according to external information detected by external-information detecting means (403, 451, 452).