In an image forming apparatus, a document image is read by an image scanner and image data are applied with image processing and stored in a memory. An image correction device corrects the image data with a different correcting condition depending on whether the image data are used for a toner image on the obverse side of the sheet or for a toner image on the reverse side of the sheet. A fixing device fixes the toner images on the obverse side and the reverse side of the sheet simultaneously.