Patent ID: 8478175

Claim:
An image forming apparatus which transfers a toner image formed on an image bearer to a sheet via a transfer belt comprising: an image bearer; a transfer belt unit which drives a transfer belt stretched out by a plurality of rollers; a transfer belt movement amount measuring portion which measures a movement amount of the transfer belt within a predetermined time between paper passing period and paper non-passage period of a sheet; a transfer belt unit position adjustment portion which adjusts a first angle with respect to a first direction of the transfer belt unit with respect to the image bearer; a roller position adjustment portion which adjusts a second angle with respect to a second direction orthogonal to the first direction of at least one of the rollers with respect to the image bearer; and a control portion which determines to use either the transfer belt unit positional adjustment portion or the roller positional adjustment portion for adjustment in accordance with a first absolute value of a first difference in a measurement movement amount of the transfer belt between paper passing period and paper non-passage period so as to reduce the first difference.