PURPOSE: To move at very low speed in axial direction a piston shaft of which one end is inserted into a cylinder discharging oil pressure.

CONSTITUTION: In a controller 16, while discharge oil pressure in a cylinder 1 is inputted, a speed command is outputted. In a variable speed control device 11 to which a speed command is inputted, a motor 10 is driven, so that rotary force of the motor 10 is transmitted to an axial driven, so that moving means 4, 8, supported by a thrust bearing 5 via a gear box 9, thereby converting it to moving force in axial direction. A piston shaft 3 of which one end is inserted into a cylinder is thus moved in axial direction. Accordingly, movement of the piston shaft 3 in axial direction is largely decelerated via the gear box 9 and the axial direction moving means 4, 8. The conversion is then made from rotation extensively adjustable by the motor 10 and the gear box 9, so that very low speed control of oil pressure oil quantity supplied to outside becomes possible.