PROBLEM TO BE SOLVED: To provide a developing device that obtains stable image quality density over the entire surface of paper.;SOLUTION: The developing device uses two-component developer using toner and carrier, and has a toner control sensor within the developing device and a patch sensor having a means for optically detecting an amount of toner attached to the surface of a photoreceptor and transfer belt. In the developing device, at least two or more toner control sensors and patch sensors for the developing device, the number of which is horizontally equal to that of the control sensors, are simultaneously moved in combination in horizontally identical position in the paper conveyance direction. They are controlled outside the width of printing paper.;COPYRIGHT: (C)2010,JPO&INPIT
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