| 摘要 |
PROBLEM TO BE SOLVED: To provide a developing device which adopts a system in which excess developer is discharged from a discharge port while the developer is supplied thereto, and develops an electrostatic latent image formed on a surface of a photoreceptor while a plurality of developing units integrally move and rotate, and for which such support that color material is not supplied excessively to the developing device without using a means for detecting concentration of the color material in the developer. SOLUTION: When determining that a density difference of a patch image is equal to or above a replenishment decision threshold, a controller 11 specifies a cause that the density difference of the patch image does not become under the replenishment decision threshold even when processing for supplying toner is repeated on the basis of the cumulative rotational frequency of a replenishment screw D5 and the cumulative rotational frequency of a conveying tool C2. COPYRIGHT: (C)2011,JPO&INPIT
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