PURPOSE: To always obtain a good transfer image quality, and to easily execute a separation of a transfer material by using an AC corona discharge which has been brought to DC bias to the same polarity as an electrification polarity of a non-image part of a photosensitive body, as a separating corona charge for peeling off the transfer material from the surface of the photosensitive body.

CONSTITUTION: An image part 4 formed on a surface layer part 5 of a photosensitive layer 1a which has been electrified positive is an area where no charge exists, because it has been formed by radiating directly a light beam, and its potential level becomes a bright potential VL. On the other hand, a non-image part 5a except the image part 4 becomes a dark potential VD of almost the same potential as the potential at the time of electrification. By using a developing electrode 2 to which a DC bias VB has been applied to the same polarity as the charge of the surface of the photosensitive body, a toner is electrified positive, the toner is attracted electrostatically to the image part 4, and a toner image 4a is formed. The potential of the image part in this case becomes VB-VL. In this regard, the developing bias VB is lower than the potential VD of the non-image part of a photosensitive body 1, but a peripheral edge part of a no-charge area of the image part 4 is induced to the negative polarity by a peripheral electric field effect by the positive charge of the non-image part, therefore, the toner is attracted satisfactorily even by the developing bias potential VB being lower than the non-image part potential VD.