Patent ID: 7197256

Claim:
An image forming apparatus comprising: a plurality of photo conductors arranged in series with a plurality of monochromatic color images formed thereon, respectively, said monochromatic color images being color components of a target color image; a transfer belt that is wound on a rotating driving roller and moves along a longitudinal direction thereof, the monochromatic color images on the photo conductors being transferred to said transfer belt sequentially and superposed on the transfer belt to form the target color image; a rotational speed control unit configured to control a rotating speed of the driving roller while making reference to rotational speed correction data so that a moving speed of the transfer belt in the longitudinal direction is maintained to be constant regardless of variation of thickness of the transfer belt in the longitudinal direction, said rotational speed correction data being created based on a relationship between a position on the transfer belt in the longitudinal direction and a thickness of the transfer bell at the position, the transfer belt including a belt information mark recorded with information used for creating the rotational speed correction data, and the rotational speed control unit including a storage unit configured to store the rotational speed correction data, a belt information reading unit configured to read the belt information mark to obtain the information used for creating the rotational speed correction data, and a correction data updating unit configured to update and store the rotational speed correction data based on the information read from the belt information mark; and a speed limitation unit configured to control the moving speed of the transfer belt when the belt information mark is read so that the moving speed of the transfer belt is lower than a usual moving speed of the transfer belt when forming the target color image.