An image processing apparatus includes an engine controller for controlling an image forming mechanism for forming an image on a sheet based on image data, a printer controller for forming image data from printing data transferred from an external apparatus, for transmitting the image data to the engine controller, and for transmitting a command for setting an operation of the engine controller to the engine controller, and a reader controller for controlling an original-reading device for outputting image data by reading an image of an original, and for transmitting the image data output from the original-reading device to the engine controller. The reader controller is provided between the printer controller and the engine controller so as to be in communication with both the printer controller and the engine controller, and so as to control an acquisition right to use the engine controller with the printer controller.