To reduce the positional deviation of respective color toner images caused by the deviation of scale factor error.

Toner marks for detecting positional deviation in respective colors formed by a plurality of electrophotographic processing parts arrayed in the moving direction of a carrying belt and forming different color image respectively, and transferred to the carrying belt are read by at least three or more sensors arrayed in a direction orthogonal to the moving direction of the carrying belt, and the positional deviation amount in a main scanning direction of other color with respect to a reference color is detected at every sensor position, and the image in the color is shifted in a reverse direction to a positional deviation direction by about 1/2 of the maximum positional deviation amount detected at the position of any sensor. Thus, remarkable color slurring is prevented from occurring due to the deviation of the scale factor error at a specified part in the image and the color slurring caused by the deviation of the scale factor error is reduced.