A variable displacement pump has a cam ring, a rotor, a plurality of vanes, a pressure plate and a rear body. The cam ring is accommodated within a pump body. The rotor rotates within the cam ring. The plurality of vanes are inserted retractably into slits formed at regular intervals circumferentially in the rotor. The pressure plate and the rear body carry the cam ring and the rotor. A circular groove communicating to a back pressure inlet bore on a bottom portion of the slits is formed in a suction area on a face of the rear body on a side of the rotor. The groove is communicated via a communication passage to a passage between a power steering gear and a tank T to introduce a working oil after used in the power steering gear.