A communication device includes a main control part configured to receive and process an image signal; a first network control part configured to convert data input from an external device into the image signal and provide the main control part with the image signal; a sub control part configured to detect a power-on command; and a second network control part configured to control communications with the external device via a network to provide the first network control part with data input from the external device. Power supplies to the main control part, the sub control part, the first network control part and the second network control part are independently controlled.