PURPOSE: To enable the surface potential of the photoreceptor to be stabilized with a simple constitution by measuring the photoreceptor current flowing in a conductive substrate and at least one external factor at the charging thereby controlling the photoreceptor current.

CONSTITUTION: An electrophotographic photoreceptor 1 has a photoconductive layer 1b on a conductive substrate 1a, this conductive substrate 1a being grounded. The photoreceptor surface potential (initial potential) at the charging of the photoreceptor 1 and photoreceptor current IPC are proportional but the proportional coefficient thereof changes with external factors such as temperature and electrostatic capacities. One of said external factors, e.g., the temperature of the photoreceptor 1, is detected with a detecting element 3 and the output thereof is connected to an arithmetic circuit 5 via output changeover circuit 4 and changeover switch SW. The output of the arithmetic circuit 5 is inputted as a control signal Vout to the power control circuit 6 of a high voltage power source HV and the supply power to the charger 2 is controlled.