Patent ID: 8831454

Claim:
An image forming apparatus comprising: photosensitive members; image forming devices configured to form toner images on said photosensitive members, respectively; a belt unit including at least an endless belt movable in contact with said photosensitive members and a first roller and a second roller rotatably supporting said endless belt; a first sensor configured to detect a position of said endless belt with respect to a widthwise direction thereof; a first inclining device configured to incline said first roller so that an output of said first sensor is kept at a first target value; a second sensor configured to detect the position of said endless belt with respect to the widthwise direction; a second inclining device configured to incline said second roller so that an output of said second sensor is kept at a second target value; an execution portion configured to execute, in a period in which said image forming devices do not form the toner images, a first test mode in which a peripheral speed of said photosensitive members is slower than a peripheral speed of said endless belt and a second test mode in which the peripheral speed of said photosensitive members is faster than the peripheral speed of said endless belt, wherein in each of the first test mode and the second test mode, said first inclining device and said second inclining devices are controlled so that an output of said first sensor keeps a first target value, and an output of said second sensor keeps a second target; and an adjusting portion configured to adjust each of the first target value and the second target value for formation of the toner images of said image forming devices on the basis of an inclination value of said first roller in the first test mode and an inclination value of said first roller in the second test mode and on the basis of an inclination value of said second roller in the first test mode and an inclination value of said second roller in the second test mode.