PURPOSE: To enable the attaching and wiring work of a terminal or the like to be simplified by transmitting a first and a second voltage waveform signal showing transmission data to a two-wire circuit, making it to be constant voltage by a reception side, simultaneously discriminating connectors connected state and recognizing received data.

CONSTITUTION: A communication control equipment 1 transmits the voltage waveform signal (a) of a binary level and the same signal (b) of which phase is inverse to each terminal equipment 2 as supply voltage and data through the D.C. current circuit 3 of the two-wire cable. Besides, a discrimination means 2-2 discriminates whether the connected state of the connectors A and B for the signals (a) and (b) is positive or negative. When it is discriminated to be positive, a recognizing means 2-3 recognizes the received data from the signal (a) and it recognizes the received data from the signal (b) when it is discriminated to be negative. Therefore, since the data can be received even by both connections and simultaneously, it is the two-wire system and the supply voltage can be also supplied, the attaching/wiring work of the terminal can be easily and surely executed.