In a variable displacement vane pump employing a cam ring, a pump rotor, and a plurality of vanes, each slidably fitted into the rotor, a biasing member is provided to force the cam ring in a direction that a geometric center of an inner peripheral surface of the cam ring and a rotation center of the rotor are spaced apart from each other. A force, by which the cam ring can be oscillated against the biasing member in accordance with a buildup of a pressure in a pump discharge portion, acts on the inner peripheral surface of the cam ring.