An image forming apparatus is provided which while ensuring obtaining an appropriate quality of images enables shortening of the warming-up period of time for the apparatus as a whole. The preliminary rotation operations of a photosensitive body and developing unit, as well as the image correcting operation followed by forming images using a test image, is prohibited. Developing conditions are determined through an immediately preceding image correcting operation followed by the formation of an image. Thereby, predicted image correction is executed which corrects them according to the lapse time as counted from the completion of the immediately preceding image-formation processing as well as the environmental conditions (relative humidity). Thereby, it is arranged that, even after warming-up for fixing has finished, the apparatus is brought to be ready for use by a user.