A variable displacement compressor comprises a flange, a movable body, and a detection sensor. The flange is joined to a housing and forms a flange passage for connecting a refrigerant passage and an external refrigerant circuit. The movable body is movably disposed in the flange, is movable according to a flow rate of refrigerant gas in the flange passage, and has a magnet. The detection sensor is fixed to or in the flange for detecting magnetic flux density of the magnet. The flow rate of the refrigerant gas is detected based on the magnetic flux density detected by the detection sensor. The flange is attachable to and detachable from the housing in a state where the flange is provided with the movable body and the detection sensor.