On an operation panel, a preview image based on first preview image data generated by a first preview image generator is displayed (first stage), and then, a preview image based on second preview image data generated by a second preview image generator is displayed (second stage). An image reducing unit reduces input image data into an image size appropriate for the preview image to generate third preview image data. When image synthesis processing is set as user setting, an image processing unit changes, in accordance with the user setting, a display aspect of at least a portion of an area on the third preview image data corresponding to an area on the input image data in which another image data (a fixed pattern or the like) is to be synthesized.