| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming device capable of forming an image of high quality by accurately measuring the concentration of toner in developer. SOLUTION: The device is provided with a toner concentration sensor 29 for measuring the toner concentration of the developing roll 23a of a developing unit which is moved to a counter position in accordance with the movement of a rotor in a non-contact state among four developing units for a rotary developing device for a color copying machine, and the toner concentration sensor 29 is arranged so as to be positioned to measure the toner concentration in a measuring area Z2 which takes a point P as a center and which is deviated from an area Z1 where a photoreceptor works when the developing roll 23a to be measured is positioned opposite to the photoreceptor, as for the part exposing from the housing 23b of the developing roll 23a to be measured. |
