An image forming apparatus is provided that makes it possible to visually identify whether or not additional information is added to image data to be output in a screen in which a preview is displayed easily. A variable resistance output dependent upon the position of the arm controls the speed of rotation of heated rollers in the lamination machine so that the layered sheet material will be drawn through the machine with variable speed to better infuse thermal adhesive into the material should such material be detected. As a result, dark current only for one line occurs in each pixel, and the dark current for one line itself can be reduced markedly.