A variable-capacity vane pump comprising a body (1) comprising a cavity (2) in which a mobile ring (3) can move, inside which a hub (4) is located which is rotatable around a fixed axis (R) and equipped with vanes (5) which during rotation are supported against an inner face of the mobile ring (3), displacing structure for moving the mobile ring (3) as a function of a control pressure between a position centered on the axis of rotation of the hub (4) and an extreme eccentric position with respect to the axis of rotation of the hub (4). According to the invention, the displacing structure of the mobile ring (3) comprise a recess (10) provided in the wall of the cavity (2) of the body (1), and a projection (9) formed on the outer face of the mobile ring (3) and designed to slide in the recess (10) of the cavity (2) of the body (1) so as to form a control chamber in which the control pressure is applied.