Abstract: A vane pump comprising a housing having front and rear surfaces and formed with a cam ring housing portion which is open to the front surface, the housing being further formed at its inner peripheral wall with recess portions and an axial bore extending from the rear surface, said axial bore being open to a center of the ring housing portion; a drive shaft freely rotatably supported in the axial bore of the housing; a rotor inserted on the drive shaft and engaged with the drive shaft, the rotor having a plurality of slits and a plurality of vanes each projectable from and retractable in the corresponding slit; a cam ring having at its inner peripheral wall a cam surface which is arranged to enclose the rotor therein and form pump chambers in cooperation with the vanes, the cam ring being formed at its outer peripheral wall with recess portions of substantially semicircular configuration in cross section; a front end plate by which the cam ring is closed at its one end; a rear end plate formed with a bearing p