Abstract: A variable displacement vane compressor for an air conditioning system used in an automobile has a cylinder assembly having a bore in which a rotor (7) is received to form at least one crescent chamber (R1, R2) between the rotor (7) and the bore. The cooling capacity is adjusted in accordance with a cooling load of the air conditioning system by displacement of an annular plate member (21) for controlling the amount of refrigerant introduced into a crescent chamber (R1, R2). The annular plate member (7) is driven by a driving units (25, 25a, 26, 27, 28, S1, S2) in which a dynamic pressure balance between a first compartment (S1) to which a refrigerant gas under a discharging pressure is introduced, and of a second compartment (S2) to which an oil under a discharging pressure is introduced.