Patent ID: 7773925

Claim:
A misregistration correcting unit correcting a misregistration of an image on an endless belt in an electrophotographic image forming apparatus, the misregistration correcting unit comprising: an image creation part configured to create a plurality of pattern sets for correcting the misregistration on the endless belt, the pattern sets each including a pattern of a plurality of mark groups arranged in a plurality of columns and a plurality of rows, the mark groups each being one of a horizontal line mark group formed of a plurality of marks each formed of a horizontal line segment and an oblique line mark group formed of a plurality of marks each formed of an oblique line segment; a position detecting part configured to detect positions of the marks; a position detection counting part configured to count a number of the detected positions of each of the mark groups and detect an abnormal one or more of the mark groups whose numbers of the detected positions are other than a prescribed number; a detection result storing part configured to store position information, the position information being information on the positions of the marks detected by the position detecting part; and a misregistration calculating part configured to calculate an amount of the misregistration based on the stored position information excluding the position information of the abnormal one or more of the mark groups.