a copying machine which detects its own condition , such as the surface potential of a photosensitive member and the toner density in a developer , and communicates with a central supervisory apparatus to transmit the detected data at a preset time or when a specified number of copies are made . the communication is controlled in accordance with the number of copies which have been made since the previous communication or the time which it has taken to make the specified number of copies since the previous communication . when the number of copies is smaller than a reference number or when the time is shorter than a reference time , the communication is canceled , or alternatively , the image forming apparatus sends the central supervisory apparatus such information . when regular communication is conducted , only items of data which have changed since the previous communication are transmitted .