To prepare pamphlets from a bundle of originals mixed with a long sideways original.

When the original is a long sideways one, its image is vertically bisected and the obtained bisected images are stored in a hard disk 108 and the originals except the long sideways original are stored as they are. A hard disk controller 104 successively reads out image data from the hard disk 108, so that when the outputted result object is folded in two at the center, the two folded ones are put in page order. Then, the images are extended on a page memory 107 two by two by a memory controller 103. When the two extended images are the bisected images obtained by bisecting one original and the bisected images are of two-page spread images, the image data of two images are transferred to a printing engine 102 as they are. In the cases other than this case, the image of a region with a fixed width corresponding to a crease part is eliminated and the obtained image data is transferred to the printing engine 102.