Patent ID: 8677156

Claim:
An image forming apparatus comprising: an image controller that performs processing of input image information; an engine controller into which a first processing part and a second processing part are combined, wherein the engine controller causes the second processing part to perform a communication regarding image formation with the image controller and controls operation of an image forming unit based on image information processed by the image controller; a power supply that supplies power to the engine controller, wherein a mode of the image forming apparatus is switchable from a first mode that is a state of image formation or a stand-by state, to a second mode whose power consumption is smaller than a power consumption of the first mode; a switch unit which switches between the first mode in which power is supplied to the second processing part from the power supply and the second mode in which power is not supplied to the second processing part from the power supply; and a communication line that transmits a notification regarding transition from the second mode to the first mode between the image controller and the first processing part, wherein the image controller and the first processing part communicate with each other through the second processing part in the first mode, or the image controller and the first processing part communicate with each other through the communication line but not through the second processing part in the second mode, wherein in the second mode, in a case where the first processing part receives a command of transition from the second mode to the first mode from the image controller through the communication line and sends back a response to the command to the image controller through the communication line, the first processing part controls the switch unit to start supplying power to the second processing part.