PURPOSE: To prevent the generation of the trouble such as the tooth skip and vibration of a timing belt due to the foreign material adhering on the belt, as for a drive transmission device equipped with a plurality of pulleys and the timing belt laid on the pulleys.

CONSTITUTION: As for a drive transmission device 25, a timing belt 30 is laid between a motor pulley 26 on a motor shaft 24a and a photosensitive body driving pulley 28 on a rotary shaft 13a for the photosensitive body. At the gear part on the inner periphery of the timing belt 30, a cleaning member 40 is pressed. In drive, the foreign materials such as the floating development agent, abrasion powder of part, and dust which adhere to the teeth part of the timing belt 30 are scraped off by a cleaning member 40.