An image forming apparatus includes an image forming unit for forming images onto sheets in either one of a first mode for sequentially forming the images onto the sheets from a last page and a second mode for sequentially forming the images onto the sheets from a front page. The apparatus also includes a rotation processing unit for rotating the image in the direction of 180.degree. for the direction of the image in the first mode before the image forming unit forms the images in the second mode. The apparatus further includes a tray for stacking the sheets, a reversing path for reversing the sheet in the second mode, a conveying path for conveying the sheets formed with the images by the image forming unit to the tray directly or through the reversing path, and a stapler for performing a stapling on an upstream side in the conveying direction in the sheet and on a left side or a right side in the conveying direction. The stapler performs the stapling on the left side in the conveying direction in the first mode and on the right side in the conveying direction in the second mode.