| 摘要 |
PROBLEM TO BE SOLVED: To suppress the fluctuation of image density caused by the fluctuation of transfer characteristics. SOLUTION: Prior to an image forming operation, a voltage value generated when a constant current of +3μA is applied on each primary transfer roller 15a to 15d by each primary transfer bias control means 202a to 202d is detected by each primary transfer bias detecting means 201a to 201d in a state where each photoreceptor drum 11a to 11d and an intermediate transfer belt 1 are rotated in a direction shown by an arrow, and then, the detected voltage value is used for the control as the primary transfer bias for the image formation and an image density detecting image. By executing the primary transfer bias control earlier than the image density control, the image density control is executed while suppressing the fluctuation of the transfer characteristics, then, the image density control is stabilized.
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