Patent ID: 7417757

Claim:
An image forming apparatus, comprising: a plurality of image forming portions transferring a yellow image, a magenta image, a cyan image, and a black image formed on a plurality of photoconductor drums to an intermediary transfer belt; a marking unit forming marks on the intermediary transfer belt; a transfer portion transferring the yellow image, the magenta image, the cyan image, and the black image on the intermediary transfer belt to a sheet conveyed on the transfer portion; a detecting unit detecting the marks with three or more sensors aligned in a direction normal to a rotating direction of the intermediary transfer belt; a calculating unit calculating an amount of color misalignment in accordance with results detected by the detecting unit; and a correcting unit correcting the color misalignment in accordance with the calculated amount of color misalignment, wherein the calculating unit calculates an amount of skew difference in accordance with results detected by two sensors among the three or more sensors, wherein one sensor of the two sensors is disposed on one end of the three or more sensors and the other sensor of the two sensors is disposed on the other end of the three or more sensors, wherein the correcting unit corrects the skew difference in accordance with the calculated amount of skew difference.