Patent ID: 8010004

Claim:
A belt transfer device comprising: a main frame; a plurality of rollers supported by the main frame; an intermediate transfer belt made of elastic material; the intermediate transfer belt running over the rollers; a transfer member for primarily transferring a toner image on an image carrier to the intermediate transfer belt; a shifter reciprocatable in specified directions so as to shift the transfer member between a transfer position where the transfer member is in compressive contact with an inner surface of the intermediate transfer belt and a home position where the transfer member is away from the belt surface; a detector for outputting a signal representing the position of the shifter in the specified directions; and a controller for determining whether the tensile force of the intermediate transfer belt is proper based on the state of the signal output from the detector while the shifter is reciprocating each time in the specified directions so as to determine whether a length of the intermediate transfer belt running over the rollers is proper; the belt transfer device being adapted to secondarily transfer the toner image on the intermediate transfer belt to a sheet of paper.