To provide a belt unit where belt deviation or meandering in an endless belt is appropriately prevented, and to provide an image forming apparatus equipped with the belt unit.

The belt unit has a plurality of rolls and an endless belt tensioned and laid by the plurality of rolls and circularly moving in a predetermined moving direction, wherein the endless belt is formed so that at least one of two edges of the endless belt overhangs to be over the end of the roll. The belt unit is provided with a rib 131 extending along the overhanging edge, and is equipped with a pulley 111 rotating coaxially with one of the plurality of rolls and provided with a groove where the rib 131 is fit to regulate a relative position of the endless belt and the roll, then it is equipped with a cleaning part 140 for cleaning the rib 131.