of the image pick up elements 14 16 18 is irradiated as the light output from a semiconductor laser 21 to a polygonal mirror 22 through an image processing unit 27 which will be described later as the polygonal mirror is rotated by scanner motor 23 the laser beam is scanned perpendicularly to the rotating direction of the photosensitive drum further photosensor 64 being situated 11 mm before the place where the laser beam starts to scan on the drum generates the signals of b and d being irradiated by the laser beam sensitizing drum 24 is charged with negative electricity by negative electrifier 25 which is supplied with the negative high voltage current from a high voltage power source then reading the exposure section 26 original chart 1 on transparent plate 2 of the original base being lighted by lighting lamps 7 6 forms the image on imaging elements 14 16 18 through mobile reflectors 9 10 lens 11 dichroic filter 12 blue filter 13 green filter 15 and red filter 17 successively the image output from the ccd as seen in the block diagram fig2 of image processing section 27 undergoes the following correction with each color i e shading correction by shading unit 28 u03b3 correction by u03b3 correction unit 29 linearization of gradient turbidity correction by masking unit 30 undercolor removing correction by ucr unit 31 gradation reproducing correction by the dither unit 32 and gradation up correction by multivalued coding unit 33 and then via laser driver.