In a variable displacement pump provided with a high pressure chamber formed at a position facing to a discharge region of a pump chamber between a back surface of a side plate and a pump casing and introducing a pump discharge side pressure oil, a low pressure chamber formed at a position facing to a suction region of the pump chamber between the back surface of the side plate and the pump casing, and communicating with a suction region of the pump chamber, and an annular seal member interposed between the back surface of the side plate and the pump casing, and surrounding the low pressure chamber together with a lubricating oil path around the pump shaft, the annular seal member is provided with a bridge portion connecting both ends of a U-shape of an approximately U-shaped portion of the annular seal member along the lubricating oil path around the pump shaft.