An image forming apparatus is provided with a display control portion for displaying a preview image of image data to be printed, and an original bundle-based processing mode is selectable by an operation portion. The display control portion, in the case of displaying a preview image in the original bundle-based processing mode, generates a thumbnail image, from image data read at each subjob, by reducing image data of a top page, and displays a thumbnail image corresponding to each generated subjob arranged as a preview image on a display portion. In addition, for changing a setting, the display control portion, in the case of displaying a preview image in the original bundle-based processing mode, displays a change key for changing only print conditions of a bundle of originals being displayed as a preview image to be selectable on the display portion by the operation portion.