a sectional view showing the main composition of an example of the copier according to the present invention first the copy process of this copier will be briefly explained a photoreceptor drum 10 on which a photosensitive layer is coated or vapor deposited is rotated clockwise by a drive means not shown while the photoreceptor drum 10 is being rotated the residual toner on the photoreceptor drum 10 is removed by a cleaning means 27 which will be explained later and a precharging exposure lamp 28 is lit so that the electrical charge remaining locally on the circumferential surface of the photoreceptor drum 10 can be removed then the photosensitive layer of the photoreceptor drum 10 is uniformly charged by a charger 16 a halogen lamp 121 mounted on a carriage 12 which horizontally slides synchronously with the rotation of the photoreceptor drum 10 irradiates document d which is set on a platen 11 light emitted by the halogen lamp is reflected on document d the reflected light passes through a slit not shown mirror 122 mirrors 131 132 mounted on a movable mirror unit 13 lens 14 and mirror 15 and then an image is formed on the photoreceptor drum 10 which will be described later that is the photoreceptor drum 10 is exposed with the light reflected on document d and an electrostatic latent image is formed on the surface the aforementioned carriage 12 and movable mirror unit 13 are driven by a stepping motor through a wire connected with the stepping motor and moved respectively in the same direction at speed v and 1 2 v next this electrostatic latent image is developed by a developing unit 17 in which toner is accommodated so that a toner image is formed on the surface of the.