PURPOSE: To prevent image blurring without complicating drive mechanism for driving an optical system by stopping the photosensitive belt surface to be exposed, and guiding original scanning light by movement of the optical system unit not relatively changing the position.

CONSTITUTION: When a start key is turned on, a unit box 47 having its end at a point C starts to move toward a point D. During its movement, a light source lamp 48 scans the contents of an original, and starts to exposed the endless photosensitive belt 45. When the end of the unit box 47 reaches the point D and finishes the scanning, the exposure of the belt 45 and its development processing are also finished at the same time. After that, the belt 45 in stop begins to move anticlockwise, and the end of the unit box 47 returns to the exposure start point C, while transfer and fixing of a copying paper 42 are processed, and the unit box 47 waits for the next copying cycle.