In an image forming apparatus and method for forming an image on plural surfaces in which the image forming sequence is practiced at the same time regardless of the type of sheets of the manuscript document which are sent from the ADF to the manuscript document reading-out apparatus and set thereon. The image information read out by scanning the first manuscript document sent from the ADF to the first reading-out position 25 at the upstream side of the manuscript document reading-out section is temporarily stored and kept therein. At the time point of finishing the scanning operation for the first manuscript document, the first manuscript document set on the first reading-out position of the manuscript document reading-out section is sent to the second reading-out position 26 at the downstream side. The second manuscript document mounted on the document mounting stand is sent to the first reading-out position. The first manuscript document transfers the toner image onto the intermediate transfer belt in accordance with the image information stored in the page memory. The second manuscript document transfers the toner image onto the intermediate transfer belt in accordance with the read-out image information. The invention relates to the image forming apparatus and method as mentioned above.