To reduce transmission of vibration of a shaft to a casing by damping it by bearings.

A first gear 4 meshing with a pinion 3 on the tip of a shaft 11a and a second gear 6 meshing with a second pinion 5 coaxial with the first gear, are arranged in a gear case 2 fitted to a bracket 1 of an electric motor. Both end of a shaft 11b to fix the first gear 4 and the second pinion 5 are supported by bearing boxes 13a and 13b through rolling bearings 12b and 12c. Both end of a shaft 11c to fix the second gear 6 are supported by bearing boxes 13c and 13d through a sliding bearing 12d and a rolling bearing 12e. A cylinder 15a composed of a vibration damping material is interposed and installed between the rolling bearing 12b and the bearing box 13a, between the bearing 12c and the bearing box 13b and between the bearing 12e and the bearing box 13d, and a flange 15f is integrally formed in the cylinder 15a. Cylinders 15b and 15c are also arranged on the bearings 12c and 12d.