PURPOSE: To suppress the generation of positive afterimages in a copying machine of a reversal developing system using a selenium photoreceptor by using an AC corona destaticizing means which is biased with the DC current component prescribed values.

CONSTITUTION: An electrostatic charger 2, a reversal developing device 4, an AC corona charger 10 for destatization prior to cleaning, a cleaning device 11, an AC corona charger 12 for destaticizing of the photoreceptor, etc. are disposed around a seleium photoreceptor 1. Here, copying is performed repeatedly by changing the biasing quantity for the DC component of the charger 12 variously. If the DC current component is biased of 0W10μA from the result thereof, the generation of positive afterimages and the fluctuations in the potential of the phototreceptor are obviated. Thus the formation of the positive afterimages is suppressed and the good destaticizing is accomplished by using such AC corona destaticizing means.