| 摘要 |
The transporting speed of a developer transporting roller is switched over depending on the condition whether a developing unit is operated for developing process or the developing unit is not in action for developing operation, and a comparable standard value for making a decision whether toner replenishment is required or not is changed based on the toner density value detected by a magnetic sensor when the developing unit is operated or is not in action for developing operation. When the developing unit has finished a predetermined number of operations, and image forming operation is suspended, a developer stirring and transporting roller is driven for a duration of time corresponding to the number of developing operations conducted, and toner density detection and toner replenishment is carried out corresponding to the toner density detected.
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