PURPOSE: To generate input saving motion with pressurization pressure as its main input by rotating a differential gear engaged with a fixed gear by thrust of a gear provided on a point of application of cylinder thrust and by axially installing a cylinder on a rotation axis.

CONSTITUTION: When a normal rotational valve 3 is set on by starting an electric motor 1 and driving a pump 2, fluid passes a normal rotational pressurization circuit 5, passes the inside of an output shaft 16 by a rotary joint and others and pressurizes a cylinder 8 uniformly. On a pressurized piston of the cylinder 8, force to draw it in the direction 25, and the piston draws a differential gear 9, and as a unidirectional clutch inside of the differential gear 9 is rotated only in the counterclockwise direction, a differential gear 10 is rotated in the clockwise direction linked. Consequently, the differential gear 10 is engaged with a fixed gear 14 and rotates a rotor 15 in the normal rotational direction. As the differential gear 9 is rotated in the counterclockwise direction in accordance with rotation of the differential gear 10, the piston of the cylinder 8 constantly keeps the same position. Consequently, it is possible to generate rotational motion of the rotor 15 only with pressurization input.