To improve the efficiency of designing or developing a controller by reducing the labor hour of designing a special controller for recognizing the use of an image forming apparatus or switching which state is displayed of a plurality of controllers.

The image forming apparatus comprises a plurality of controllers 22, 23 corresponding to a plurality of external units for converting image information from the plurality of external units 24, 25 for generating the image information, and an engine controller 21 for controlling the image forming operation based on the image signal, where the engine controller recognizes the use of the apparatus for either of the plurality of controllers 22, 23 and switches which of the images is formed based on the signal from either the controller 22 or 23.