PURPOSE: To make the potential of a photosensitive body uniform by omitting test printing action after exchange, by conducting light irradiation by means of a light irradiation deelectrication means while a photosensitive drum is being rotated for a fixed time, after a photosensitive body drum unit has been exchanged.

CONSTITUTION: When a photosensitive body drum unit 3 has been exchanged, whether or not the upper part cover of a main body 1 is closed is detected. When it is detected that the upper part cover is closed, the rotary movement of a photosensitive drum 2 is started, and then, light irradiation is started by means of a light irradiation deelectrification means 6. Next, whether or not a time necessary for making the photoconductive layer (photosensitive body) potential of the drum 2 uniform has passed is detected, and when it is detected that the necessary time has passed, photoirradiation by means of the means 6 is finished, and the rotary movement of the drum 2 is stopped.