When a cleaner is included exclusively for cleaning a transfer/transport belt to remove toner therefrom, the structure of an image forming apparatus becomes complex and the costs thereof increase. The present invention attempts to remedy this situation. Specifically, a difference between a peripheral speed relative to the transfer/transport belt to be set for cleaning and a peripheral speed relative to photosensitive drums to be set therefor is made larger than that between peripheral speeds to be set for ordinary image formation. Because of this constituent feature, unnecessary toner on the transfer/transport belt is efficiently transferred onto the photosensitive drums on a stable basis for a short period of time.