PURPOSE: To adjust the potential by electrification of a photosensitive drum to the potential buitable for the characteristic of each of toner by changing the number of electrifying electrodes used.

CONSTITUTION: This device is provided with impressing electrodes 2a-2c on the surface of an insulator 1 whose surface is smooth such as a glass, and further, the electrifying electrodes 3a-3c of the semiconductor film whose volume resistivity is for instance, 105-1013Ωcm on the surfaces of the impressing electrodes 2a-2c. And the device is constituted so that a high voltage power source 5 is connected to the impressing electrode 2a so as to generate a corona discharge between the electrifying electrode 3a and the photosensitive drum 4, and the high voltage power source 5 is connected to the impressing electrodes 2b and 2c through switches 6b and 6c, and when the switches 6b and 6c are closed, the corona discharge is generated between the electrifying electrodes 3b and 3c and the photosensitive drum 4, thereby the photosensitive drum 4 can be set at the potential by the electrification adjusted to the characteristic of each of the toner.