1. An image forming apparatus, comprising: an image forming station for conveying a sheet material along a stationary lateral reference position and for forming an image on the sheet material; refeeding means for refeeding to said image forming station the sheet material on which the image has been formed in said image forming station; means, provided in said sheet refeeding means, for shifting the sheet material in the lateral direction from the stationary lateral reference position by a predetermined amount, wherein the amount of the shift is predetermined on the basis of a change in a lateral dimension of the sheet material resulting from an image forming operation in said image forming station.