In an image forming apparatus and a control method thereof according to this invention, in a case that a received print job designates image formation on a surface of a sheet on which an image has been formed, whether image formation on the sheet based on the print job is possible is determined based on at least image information of the sheet acquired by reading the image of the sheet. If it is determined that image formation on the sheet based on the print job is impossible, the image formation on the sheet is stopped. If it is determined that the image formation on the sheet based on the print job is possible, an image is formed on the sheet in accordance with the image information of the print job.