To effectively prevent an inclination of a gear without complicating the support structure of the gear when making a rotating shaft for axially supporting a roller which is large in inertia mass fitted with one of paired gears in a floating state in order to reduce gear noise resulting from geometric engagement errors of the paired reduction gears.

The tooth-width direction center of a hub 32a arranged at a reduction drive gear 32 of a reduction gear mechanism 31 is spline-fitted (43a, 44a) with a secondary pulley shaft 9b in the axial direction in the floating state, and both ends of the hub are fitted (43b, 43c, 44b and 44c) with the secondary pulley shaft 9b in a seal case manner. The axial both ends of the hub 32a are fitted with the secondary pulley shaft 9b in the seal case manner, so that the inclination of the reduction drive gear 32 can effectively be prevented.