PURPOSE: To lead out the reflected light from the same point of the original to plural points by forming such an optical system as the one wherein scanning exposure light transmits from the first face to the second face and from the second face to the first face of the image forming through-lens system.

CONSTITUTION: The reflected light from the original 0 by integral pentagonal roof type plane mirros 11, 16, plain mirrors 12, 17 making scan-movement is reflected by the plain mirros 11, 16. One reflected light is then reflected by the plain mirror 12 and enters from one face of an image forming through-lens system 10 and emits from the other face. The other likewise enters from the other face of the lens system 10 and emits from one face, becoming two sets of the scan-reflected light for the same point of the original. Exposure of the same point of the original is simultaneously accomplished to photoreceptors 2, 3 by the optical light of these two sets of the reflected light by the plain mirrors 13 thru 15 and 18, 19, etc., whereby the formation of the color images, etc. may be satisfactorily accomplished. Simultaneous exposure of plural sets may be performed in the similar manner according to the configuration, etc. of the plain mirrors by splitting the exit light of the lens system 10 with half mirrors, etc