A vane pump includes a rotor having slits, vanes received in the slits, a cam ring having an inner circumference cam face with which the vanes are brought into sliding contact, side members, pump chamber formed by the rotor, the cam ring, adjacent vanes, and back pressure chambers formed in the slits by the vanes. In the vane pump, the side members are provided with back pressure opening portions opening at sliding-contact surfaces in sliding contact with the rotor, the back pressure opening portions being configured to communicate with the back pressure chambers, and protruding opening portions protruding along the rotating direction of the rotor from end portions of the back pressure opening portions on the communication-finishing side. And inner-side inner circumferential surfaces of the protruding opening portions are respectively connected to inner-side inner circumferential surfaces of the back pressure opening portions.