Image forming apparatus having a plurality of developing devices

摘要

The apparatus includes a photosensitive drum, a charger for charging the drum, a plurality of developing devices, selecting switch for selecting one of the developing devices to be used and controller for controlling the output of the charger so as to elevate the surface potential of the drum by a predetermined potential corresponding to the selection by the selecting switch, said predetermined potential being equal to a decay potential occurring while the surface of the drum rotates from the position opposed to the charger to the portion opposed to the selected developing device.