To enable an endless belt made of a metal to span with a proper tension between pulleys and enable suppression of the occurrence of coming off of a wheel and zigzagging.

A reduction gear 81 transmits a rotation drive force to a drum shaft through a steel belt 84 spanning between an input pulley 83, fixed on a motor shaft 82 connected to a drive motor M, and an output pulley 85 fixed on a drive output shaft 86 connected to a drum shaft 20a of a photoreceptor drum. The motor shaft and the drive output shaft are journalled to a first frame 88a and a second frame 88b. Since the frames are constituted separately from a side plate 29 to support the drum shaft, holes for bearing parts 88c and 88d can be machined in a frame being far smaller than the side plate. Accordingly, the holes for the bearing parts can be machined by using a high performance machining device. Thus, a wheel base between the motor shaft and the drive output shaft and precision of parallelism between shafts can be improved.