PURPOSE: To eliminate the need for a cleaning a device dedicated to a transfer roller, to reduce cost and to miniatualize a device by providing an area detecting means, a potential applying means and a potential control means.
CONSTITUTION: A toner picture formed on a photosensitive body by developing an electrostatic latent image is transferred onto transfer paper 8 by the transfer roller 5. When the area detecting means detects that the transfer roller 5 faces the picture area where the toner picture is formed on the surface of the photosensitive body 1, the potential control means 12 controls the potential applying means 11 so that the potential of the transfer roller is higher than that of the photosensitive body 1. When the photosensitive body 1 rotates further and the area detecting means detects that the transfer roller faces a non-picture area, a part other than the picture area on the photosensitive body, the potential control means 12 controls the potential applying means 11 so that the potential of the transfer roller 5 is lower than that of the photosensitive body. Consequently, the need for the operation of the cleaning device removing the toner of the transfer roller 5 is eliminated, thus the need for the cleaning device dedicated to the transfer roller is eliminated.