Patent ID: 7133056

Claim:
An image forming apparatus comprising: plural image forming sections; and a carrying belt on which primary images formed on the plural image forming sections respectively are transferred and superimposed, wherein the image forming apparatus further comprises: a test pattern forming device for forming test patterns on the carrying belt by using the plural image forming sections; a pattern sensor for reading a test pattern on the carrying belt; a positional shift calculating device for calculating positional shift quantity of main scanning direction and that of sub scanning direction basing on read result by the pattern sensor with respect to at least one correction target color; a correction quantity determining device for determining correction quantity of each scanning direction with respect to a correction target color(s) basing on positional shift quantity of each scanning direction calculated by the positional shift calculating device and reliability coefficient of each scanning direction; and a positional correction device for conducting positional correction basing on correction quantity determined by the correction quantity determining device with respect to an images of a correction target color(s), out of respective images to be formed by the plural image forming sections, and reliability coefficients used by the correction quantity determining device differ by a main scanning direction and a sub scanning direction.