To stably and uniformly electrify an image carrier all the time, without causing an abnormal discharge such as a white streak and dot by preventing the soiling of an electrifying member.

An electrifying roller 2 is provided in proximity to a photoreceptor drum 1 and a preprocessing roller 3 is provided on the upstream side from the electrifying roller 2. Then, a voltage constituted in such a manner that AC and DC voltages are superimposed is applied to the electrifying roller 2 by a power source circuit 4. Further, the voltage constituted in such a manner that the AC and DC voltages are superimposed is applied to the preprocessing roller 3 by a second power source circuit 5. When the DC voltage applied to the electrifying roller 2 in an image region is defined as DC1, the DC voltage applied to the electrifying roller 2 in a nonimage region is defined as DC2 and the DC component voltage of the voltage applied to the roller 3 is defined as D3, the conditions of DCI>DC2>DC3 can be satisfied.