In an image forming apparatus, an image forming contrast potential for obtaining the maximum density is set by reading a specific pattern transferred and formed on a sheet. A photosensor detects the density of a specific pattern formed on an image carrier at the image forming contrast potential, and the detection result is stored. A correction amount for the image forming contrast potential is calculated on the basis of the relationship between the stored detected density, and the density, detected by the optical sensor, of the specific pattern formed on the image carrier at a predetermined timing. The image forming contrast potential is adjusted by the correction amount.