Abstract: An electrophotographic copying apparatus which includes a photosensitive member or photoreceptor which is repeatedly utilized for formation of electrostatic latent images on it, a device for forming an electrostatic latent image on a photoreceptor surface, a device for detecting conditions affecting the operating characteristics of the photoreceptor, a device for determining the state of operation of the image forming device according to the conditions detected by the detecting device, the conditions being in a predetermined relationship which is specifically represented by a predetermined reference equation, a device for correcting the state of operation of the image forming device so as to render a potential of the latent image formed on the photoreceptor surface substantially constant, and a device for successively revising the reference equation based on the conditions detected by the detecting device and the state of operation which has been corrected by the correcting device.