1. An image forming apparatus comprising: an image forming unit arranged to form images on a first side and a second side of a continuous sheet; and a control unit arranged to control the image forming unit so as to form images based on image information and to form maintenance images for maintaining the image forming unit, wherein the control unit is arranged to control the image forming unit so as to form images on the second side of the sheet after forming images on the first side of the sheet, and so as to form the maintenance images on the second side at positions such that the maintenance images do not overlap with the images based on the image information formed on the first side.