PURPOSE: To reduce the trouble of wiring construction by transmitting a coded ultrasonic wave signal through the piping of control wiring and employing resistive termination to ultrasonic waves on a reception side.

CONSTITUTION: When a power wiring controller is controlled by the coded ultrasonic wave based upon time as a variable, an ultrasonic transmitter 31 is fitted on a wall 30 and the coded ultrasonic wave signal is transmitted through a hollow wiring duct 37. The transmitter 31 consists of an oscillation circuit body 32, pushon switch 33, battery 34, and microphone 35 for ultrasonic wave transmission, and the coded ultrasonic wave generated by the operation of the switch 33 is led to the duct 37 through a reflector 36. The ultrasonic wave duct 41 is so constituted that a signal from an ultrasonic wave signal oscillation circuit 38 is sent in the ultrasonic wave duct 41 through a transmitting microphone 39 and received by a receiving circuit 42 through a receiving microphone 44. Resistive terminals 40 and 43 are provided on the transmission and reception sides of the duct 41 to prevent the generation of code distortion due to reflection.