To obtain a power transmission which continues driving a load even when a motor driving the load is broken, and reduces power consumption when driven at a low speed as compared with the maximum operation speed.

The power transmission is constituted by installing a plurality of motors constituting an actuator for driving the load in relation to one load and providing a reduction gear train transmitting the rotary driving force of the motor and reducing speed. The motors 101 are composed of a first motor 101a and a second motor 101b, and the first motor 101a is coaxially connected through a clutch 101c to the second motor 101b. When the load is heavy, two motors are driven, and when the load is light, for example, only the first motor 101a is driven and the clutch 101c is disconnected to separate the second motor 101b.