devices 1A and 1B and the personal computers 2A to 2D are connected to the existing network NW. In addition, the power line communication apparatus 10 feeds power to the multi-function machine 1B.Thus, even when the multi-function devices 1A and 1B are used as network printers of the personal computers 2A to 2D, this exemplary embodiment may be applied.Further, various kinds of processes described