In a variable displacement pump, a first groove always connected to a second hydraulic chamber is provided in a slide surface of a cam ring facing to an end surface of a side plate, and a second groove always connected to a suction port is provided in the end surface of the side plate, whereby when the cam ring is moved to a moving end side in which a volumetric capacity of a pump chamber is reduced, the first groove and the second groove are connected, and the second hydraulic chamber can be connected to the suction port by the grooves.