PURPOSE: To reduce the fluctuation of rotation and to prevent the biasing of a photosensitive belt by driving and rotating the photosensitive belt in a timing belt system and providing a flange or a deviation stop guide.

CONSTITUTION: A wide timing belt 6 is constituted inside the photo-sensitive belt 3 and timing pulley-like driving rollers 2A and 4A for driving the belt 6 mesh with the belt 6. The flanges 7 for stopping the deviation are provided at both ends of the respective rollers 2A and 4A so as to regulate the side end face 6A of the belt 6 and prevent the deviation of the belt. When the device is constituted so that sprockets 8 are respectively fixed by shaft to be turned at both ends of supporting shafts 2a and 4a, a driving roller and a follower roller are not needed. In such a case, on a cap type deviation stop guide 9, a groove 9A in which the end 3A of the belt 3 is fitted is engraved on its side end face 9C and tooth-shaped recessed part 9B meshing with the sprocket 8 is formed at the pitch of equal interval, then the timing belt is obtained. Since the belt is driven to travel in the timing belt system, the difference of tension at both ends of the photosensitive belt is prevented, the fluctuation of rotation is reduced and the biasing is prevented.