An image forming apparatus includes a transfer unit having an endless transfer belt stretched over a plurality of rollers, a pair of integrated support side plates for supporting the plurality of rollers rotatably, a pair of press side plates supported, to be able to rotate in the direction of moving toward or away from the image carrier, by means of a supporting member provided in the frame of the transfer unit, a swing portion provided on the press side plates and supporting the support side plates swingably with respect to the image carriers when the transfer belt and the image carriers are pressed, and a member for urging the press side plates in the direction that the transfer belt presses the image carrier.