PURPOSE: To match the timing of transmitting to that of receiving by supplying a rectangular voltage,corresponding to a timing pulse to be output from a machine side microcomputer and superposed with a DC voltage, to a remote controller side, and detecting at the controller side the rectangular voltage superposed on an input voltage, and inputting the pulse to a microcomputer on the controller side.

CONSTITUTION: Microcomputers 4, 5 are disposed at the sides of a remote controller 1 and an apparatus 2. DC power sources V1, V2 are provided at the apparatus 2. For example, the V1 is set to about 12V, and the V2 is set to about 20V. A voltage waveform to be supplied to the controller 1 through a power line 3a is obtained by superposing a rectangular voltage on the voltage 12V from the power source V1. When the rectangular voltage superposed on the input voltage is detected by a detector 9, a timing pulse (rectangular wave) synchronized with the timing pulse output from the microcomputer 5 is input to the microcomputer 4, read by the microcomputer 4, the timing of transmitting and receiving a data signal is matched to the rising of the pulse, and the timings of communicating the data signal between the controller 1 and the apparatus 2 are brought into coincidence.