A cartridge vane pump includes: a side plate brought into contact with first end surfaces of the rotor and the cam ring; a cover brought into contact with second end surfaces of the rotor and the cam ring, the cover attached to the body; and an O-ring provided in an outer circumference of the side plate, the O-ring being configured to seal a gap between the outer circumference of the side plate and an inner circumference of the body. The side plate has: a first flange portion configured to restrict movement of the O-ring towards the rotor side; a second flange portion configured to restrict movement of the O-ring towards an opposite side from the rotor. The first flange portion is formed to be able to compress the O-ring with the body in an axial direction of the driving shaft.