To provide a closed-type horizontal position adjuster for an automobile provided with a pump 6 feeding a pressure medium from a pressure medium storage container 4 to pressure medium chambers 2a-2d or feeding it through the opposite route.

When the pressure medium is supplied from the pressure medium storage container 4 to the pressure medium chambers 2a-2d, an inlet 8 of the pump 6 is connected to the pressure medium storage container 4 and to the pressure medium chambers 2a-2d via an outlet 10 of the pump 6. Contrarily, if pressure air should be supplied from the pressure medium chambers 2a-2d to the pressure medium storage container 4, the inlet 8 of the pump 6 is connected to the pressure medium storage container 4 and to it via the outlet 10 of the pump 6. This connection is carried out by means of the controllable directional valves 14, 18. The horizontal position adjuster enables the pump 6 to be always operated only in one direction.