PURPOSE: To detect automatically the size of a nonstandard original, by providing a band-shaped light emitting element on the lower face of an opening and closing cover on an original set table.

CONSTITUTION: A band-shaped light emitting element (such as an electroluminescee) is provided along a direction (a) of the movement of an optical illumination system 4 on the lower face of a cover 3 of an original set table 2. When an original 6 is set and the cover 3 is closed to start the copy, the optical illumination system is moved in the direction (a). Since the optical illumination system 4 is provided with a photo detecting device 8, the light of the light emitting element 5 intercepted by the original before this movement is detected by the photodetector 8 when the optical illumination system is moved to the end of the original. The distance of the movement time of the optical illumianation system till the detection of the light of the light emitting element is covered to pulses, and the number of these pulses is collated with the number of pulses corresponding to a preliminarily inputted original size to detect automatically the size of the set original, and as the result, a copy from is automatically selected and supplied.