The invention relates to an actuator comprising a stationary structure and an actuating element that is movable relative to the stationary structure, a device for locking the actuating element in position which is mounted on the stationary structure and has a state for locking and a state for releasing the actuating element. The locking device comprises, successively, a stress limiter and at least one locking element so arranged as to be butting against one surface of the actuating element, in order to oppose a motion of the actuating element in a predetermined direction. The actuator comprises a member for controlling the locking device in the releasing state thereof and a member for resiliently returning the locking device to the locking state thereof.