To provide a gear saving space by using a less number of components and allowing easy assembling work by losely fitting the gear to a bearing.

The gear for an idler or the like has an inner diameter fitted to the outer ring, with a fit quality of Js6 or so, of the bearing fitted to a fixed shaft. The gear is mounted on the outer ring of the bearing with a plurality of bolts. A plurality of socket bolts are used instead of the plurality of bolts.