PURPOSE: To secure large torque and low speed simultaneously with small torque and high speed by setting a brake piston to actuation and/or inoperativeness, making a bracket rotable or fixable and using a high speed motor and a reduction-geared motor in a selective manner.

CONSTITUTION: When a large torque and low speed rotation is outputted, a pressure medium is taken into a cylinder groove 72 from an inlet hole 18, operating a brake piston 17, and a brake disk 21 is held between both movable stationary plates 19 and 20, thereby checking any rotation of a bracket 10. If so, an internal gear 101 is fixed, while a planetary reduction gear mechanism is constituted of a sun gear 16, a planetary gear 11, and the internal gear 101, and output speed of a reduction-geared motor 14 is decelerated and transmitted to an output shaft 8 via a carrier 13. When the output rotation of high speed and low torque is secured, the pressure medium to be taken into the cylinder groove 72 is extracted. If so, the holding of the brake disk 21 between both stationary plates 19 and 20 is released, so that the bracket 10 becomes rotatable. In succession, a high-speed motor 1 is rotated.