PURPOSE: To control turn-on/turn-off of a power source without providing a control line, by sending out a turn-on/turn-off control signal by superposing it on a power source cord which is connected between a terminal equipment and a convenience outlet box, when sending said signal from the terminal equipment to the convenience outlet box.

CONSTITUTION: A terminal equipment 1 is provided with a terminal power source circuit 8 and a device interface part 9, and also constituted by adding a power source control signal generating circuit 22 and a signal superposing circuit 25. Also, a convenience outlet box (power source control mechanism) 15 is constituted of a power source switching circuit 19, a signal detecting circuit 26 and a signal decoding circuit 28, and also, devices 2, 3 are connected to the convenience outlet box 15 and the terminal equipment 1 by power source codes 13, 14 and signal cables 10, 11. In such a state, the signal generating circuit 22 is controlled by a control program and sends out a control signal of turn-on/turn-off of a device power source. This signal is sent to the convenience outlet box 15 from a power source. This signal is sent to the convenience outlet box 15 from a power source cord 12, as a high frequency component by the signal superposing circuit 25, and a power source switch of the devices 2, 3 is turned on and off.