On each of the two longitudinal sides of the cushion (2) of a seat (1) there is provided a front mechanism (4) and a rear lever (5) to move the seat, varying the height and inclination thereof. The rear lever (5) is hinged to the cushion (2) and to a rear supporting bracket (7). The hinging axis (a1) between the rear lever (5) and the cushion (2), is located at a lower position than the horizontal hinging axis (a2) between the rear lever (5) and the rear supporting bracket (7).