An image forming apparatus which can improve image formation capability to a satisfactory degree while curbing the rise in running cost. An image forming device forms adjustment images having different densities on an image support member having a higher optical reflectivity than an optical reflectivity of the adjustment images. A reading reads the adjustment images. An output from the reading device is read at a predetermined number of readings or time interval between readings based on the densities of the adjustment images susceptible to the optical reflectivity of the image support member.