Abstract: The jack comprises a tubular primary screw (10) provided with an outer screw thread and an inner screw thread having opposite thread hands, a secondary screw (11) cooperative with the inner screw thread and having an end (11a) articulated to a fixed point, a nut (9) fixed in rotation and connected to move in translation with the element to be adjusted and cooperative with the outer screw thread, a speed reducer associated with a motor (M) for driving the primary screw (10) in rotation, and means for preventing a rotation of the speed reducer (13) relative to the nut (9). These means comprise an articulated compass structure (18) having two branches (18a, 18b) articulated together. One of the branches is also articulated to the speed reducer (13) while the other branch is articulated to a part (9) of the jack which is fixed in rotation. The compass structure (18) considerably reduces the friction and improves the efficiency of the jack.