Patent ID: 7308212

Claim:
A color image forming apparatus, comprising: an intermediate transfer member; a plurality of image forming sections provided along the intermediate transfer member; a primary transfer device provided along the intermediate transfer member to transfer toner images formed on each the image forming section so that the toner images are superimposed on the intermediate transfer member; a secondary transfer device provided at the downstream side of the primary transfer device to transfer superimposed toner images through a bias voltage; a discharging device having a grid and a discharge electrode provided between the primary transfer device and secondary transfer device; an image density sensor provided along the intermediate transfer member to detect an amount of toner adhesion on the intermediate transfer member; a control device to control applied voltage for the discharge electrode in accordance with output of the image density sensor, wherein a patch image having a prescribed uniform density is formed and transferred onto the intermediate transfer member with a lower primary transfer current value than a normal primary transfer current value.