A swash plate type variable displacement compressor is disclosed for adjusting an inclined angle of a swash plate (13) placed in a crank chamber (2a) in accordance with a pressure difference between the crank chamber (2a) and a gas suction chamber (4a) and for compressing gas supplied to compression chambers (18) from the gas suction chamber (4a) by pistons (21) that reciprocate with a stroke according to the inclined angle of the swash plate (13) in order to thereby control a volume of gas to be discharged from a gas discharge chamber (4b). A communication passage (23) connects the gas discharge chamber (4b) to the gas suction chamber (4a), and a branch passage (24) branching from the communication passage (23) is connected to the crank chamber (2a). Disposed in the communication passage (23) is a valve (25, 45) which normally blocks the communication passage (23) and opens the communication passage (23) to alter pressure in the crank chamber (2a).