PURPOSE: To prevent impression flaws on a photosensitive belt and the occurrence of toner filming and to prevent the damage of the photosensitive belt for attachment and detachment of a cleaning unit and a photosensitive body unit by displacing a backup member so that the photosensitive belt is separated from a cleaning brush when the copy mode is terminated.

CONSTITUTION: In the copy mode, a backup member 3 pressurizes the rear face of a photosensitive belt 1, and a magnetic brush 23 keeps such a proper gap that the magnetic brush is attracted to an iron pipe 31 of the backup member 3 to remove effectively an unnecessary toner 13 on the photosensitive belt 1. Though the attraction is too strong and iron powder storing the unnecessary toner is not moved if a nonmagnetic material 32 does not exist on the surface of the backup member 3, tips of bristles of the magnetic brush 23 are orthogonal to the moving direction of the photosensitive belt to improve the barricade effect and the cleaning capacity is improved because the nonmagnetic material 32 exists in this case.