To provide a vane push-up mechanism for a vane pump having a cam ring provided with a circular slide contact surface of simplified structure, and reduced leak, torque loss, and abrasion.

A rotor cut part 11 is formed along a rotor outer circumference 2a to have a larger diameter than a bottom part 3b of a vane 3 engaged in a radial groove 6 in a rotor 2 to be capable of protruding and retracting when the vane 3 is protruding from the groove 6 to the maximum, a circular hole (lock part) 12 is provided in the vane 3 to be positioned between a slide surface 4a of a cam ring 4 and the rotor cut part 11 and to be concentric to the slide contact surface 4a of the cam ring 4 as the vane 3 is applied to the slide contact surface 4a of the cam ring 4, and a linear circular ring 13 of the same cross sectional form as the circular hole 12 in the vane 3 is engaged and inserted into the circular hole 12 to be disposed in such a way that the circular ring 13 and the lock part 12 will not interfere with the rotor 2. By properly introducing pressure fluid to the bottom part 3b of the vane 3, pressure balance of the vane 3 is adjusted.