Abstract: An oil pump includes pump constituent elements, a pump body, and a driving shaft. The pump constituent elements define a pump chamber between a rotor and a cam ring that houses the rotor. The pump body is constituted by a front body and a rear body. The front body defines a housing space for housing the pump constituent elements. The driving shaft extends through and is axially supported by the front body to rotatably drive the rotor. An annular space is formed around the driving shaft in the front body, between a bearing for rotatably driving the driving shaft of the front body, and the pump chamber of the pump constituent elements. A flow control valve is placed in the annular space to return part of a pump discharge fluid from the pump chamber to a pump suction side.