| 摘要 |
PURPOSE:To prevent the image density of an output image form decreasing even if where is a developing device to which a developer can not be supplied by providing a control means which corrects a developing bias voltage applied to a developing means and a primary high voltage applied to an image carrier to corrected values. CONSTITUTION:A decrease in developer concentration is divided into plural stepwise ranges according to constant data in advance, and corrected values of developing bias voltages or primary high voltages corresponding to the respective ranges are stored previously in a ROM 602. Then even if the developer concentration of each developing device drops, a developer is not supplied immediately, and the developing bias voltage or primary high voltage is corrected during the use of a developing device only when the developer concentration of the developing device to which a developer can not be supplemented decreases according to the position relation of an angle of rotation in continuous copying operation. Consequently, even if there is the developing means to which the developer can not be supplemented from a developer supplementing means during the execution of the sequence of image formation, the image density of an output image does not decrease and the image has high quality. |
