1. An image forming apparatus forming a visible image on a recording medium, comprising: a functional element required for an image forming operation; a first control unit controlling the functional element; an input unit inputting an external instruction; and a second control unit communicating with the first control unit about information on the image, performing a process in accordance with the instruction input via the input unit, and outputting a return signal for starting the functional element required for performing the process in accordance with the instruction.