To reduce backlash in between the teeth of a drive.

The rotational motion of a motor output shaft 1 is transmitted to a large motor gear 2. The large motor gear 2 is engaged with small motor gears 3a, 3b, and transmits the rotational motion of the motor output shaft 1 to these gears. The rotational motion motor transmitted to the small gears 3a, 3b is decelerated by harmonic drives 4a, 4b, and is outputted to small gears 5a, 5b directly coupled with the harmonic drive output shaft. The rotational motion of the small gears 5a, 5b directly coupled with the harmonic drive output shaft is transmitted to a large gear 6 directly coupled with a load shaft, engaged with them, and is them transmitted to a load shaft 7 connected with a load. When the small motor gear 3b is fixed to the rotational shaft (I axis) of the harmonic drive 4b, rotational force in a specified direction is applied to the I axis before doing so. As a result, backlash in between the gears can be eliminated.