To provide a network in a house which is safe and can be conveniently constructed.

A high voltage outputting part 21 outputs an alternating current signal wherein the effective value to be supplied to an electric appliance in a house is higher than 100 V alternating current signal, for example, an alternating current signal whose effective value is 102 V. Similarly, a low voltage outputting part 22 outputs an alternating current signal, for example, the effective value of which is 98 V. A switch 23 switches and outputs the alternating current signals under control of a switch controlling part 24. Even though the switch controlling part 24 controls the switch 23 on the basis of data to be transmitted, when the data is 1, an output from the high voltage outputting part 21 is controlled so as to be outputted, and when the data is 0, an output from the low voltage outputting part 22 is controlled so as to be outputted respectively. A signal outputted from the switch 23 is superimposed on a signal of a power supply voltage to be supplied to the electric appliance and supplied to the electric appliance.