| 摘要 |
PURPOSE:To detect toner concentration accurately by a toner concentration sensor, and maintain excellent image quality by arranging the toner concentration sensor below the vicinity of a discharge part. CONSTITUTION:When transfer operation is repeated, toner in a developer housed in a developing tank 16 of a developing device 8 is consumed gradually, and a ratio of the toner to a carrier, that is, toner concentration is reduced. A toner concentration sensor 34 is arranged in the developing tank 16 so as to detect a change in this toner concentration, and driving control of a toner replenishing roller 21 based on this toner concentration sensor 34 is carried out by a control device 32. The toner concentration sensor 34 is arranged in the lower wall part of the developing tank 16 below the vicinity of a discharge opening 24, that is, in the bottom wall part 16c in the vicinity of the discharge opening 24 formed in the side wall part 16b. Thereby, the toner concentration can be detected accurately by the toner concentration sensor 34. |
