An image forming apparatus includes first through third control units, with the first for processing input image information and each of the second and third for controlling an operation of an image forming unit by communication with the first. In a first mode, in which power is supplied to the first through third control units, the first and third control units communicate via the second control unit. In a second mode, in which the first control unit does not communicate with the second control unit, the first and third control units communicate via a communication line without communicating via the second control unit. The power consumption of the second mode is lower than that of the first mode. In the second mode, the first and third control units can transmit information for transition from the second mode to the first mode to each other via the communication line.