1. A hydraulic actuator comprising a variable-delivery positive-displacement pump, a first directional-control valve commanded on the basis of an actuator movement instruction, and a ram supplied by the first directional-control valve, the pump comprising a mobile member a movement of which allows a delivery of the pump to be continuously varied, the member being able to be moved by the ram, the first directional-control valve being able to apply a continuous function linking the movement instruction to the delivery of the pump via the position of the member as it moves, wherein the actuator comprises a second directional-control valve commanded on the basis of an output pressure (P) of the pump, the second directional-control valve comprising two positions, a rest position, obtained as long as the output pressure (P) of the pump is below a predetermined pressure and transmitting the output pressure (P) from the first directional-control valve directly to the double-acting ram, thereby allowing the pump to follow the continuous function and, an active position, obtained when the output pressure (P) of the pump is greater than or equal to the predetermined pressure and transmitting the output pressure (P) of the pump to the ram so as to reduce the output pressure (P) of the pump without passing via the first directional-control valve and without following the continuous function, wherein the member is configured to allow the pump to reverse the direction of its delivery, wherein the ram comprises two chambers and in that the actuator comprises a third directional-control valve configured to transmit the output pressure (P) of the pump either to one or the other of the two chambers according to the direction of the delivery of the pump.