| 摘要 |
A color image forming apparatus including tandem type image forming units that form images of different colors, respectively. The image forming units form test marks of different colors on a conveyor belt in its conveying direction at predetermined intervals. The test marks include linear position displacement detecting test marks and density detecting test marks. Each of the linear position displacement detecting test marks extends in a direction perpendicular to the conveying direction of the conveyor belt, and each of the density detecting test marks includes an area having a predetermined density and being adjacent to each of the linear position displacement detecting test marks. A detection operation for detecting position displacements of the linear position displacement detecting test marks in a sub-scanning direction of the conveyor belt and a detection operation for detecting densities of the density detecting test marks are performed, based on detection signals output from sensors.
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