PURPOSE: To reduce the number of used mirrors and to reduce the cost considerably by providing a means where variable magnifications are inputted, a means which controls the position of an optical system to drive a lens, and a means which controls the timing of paper supply.

CONSTITUTION: A device is so constituted that the first mirror 11 and a lens 12 are moved on a basis of a photosensitive drum 14 in case of varying of magnification, and extents of movement ΔM and ΔL are calculated when a reduction magnification is inputted. The first mirror 11 is moved left for the extent ΔM, and the scanning start position of a moving platen 10 is separated from the position of the mirror 11, and the time spent in scanning for the extent ΔM is longer than that for unmagnification. Scanning is performed with a platen signal, and paper is supplied with a form start signal when a set time t2 obtained by calculation elapses, and the front end of the form is positioned, and copying without positional slippage is executed. Consequently, expenses required for high- precision attachment of mirrors are reduced considerably because only two mirrors 11 and 13 are used.