PURPOSE: To achieve uniform electrification at all times and to obtain a satisfac tory image by providing a preliminary drive means which, during the period of time that image formation is not carried out, rotates and drives only an image carrier at speed lower than the speed at which it is rotated during the image formation.

CONSTITUTION: A drum drive pulley 25 incorporating a clutch is attached to one end of a photosensitive drum in an axial direction and rotates and drives the drum by means of a motor 24. On the other hand, the power of a main motor 23 is transmitted to the drum drive pulley 25 by means of a drum-drive timing belt 26. In this case, the preliminary drive means is composed of the drum drive pulley 25 and the drum drive motor 24. During the period of time that the image formation is not carried out, only the photosensitive drum is rotated and driven by the preliminary drive means at speed lower than the speed at which it is rotated during the image formation; thereby, the photosensitive drum and an electrifying roller rotate while one follows the other in contact with each other at all times. Thus, partial temperature-difference in the electrifying roller and the occurrence of a trace made by the contact of the photosensitive drum and the electrifying roller are prevented.