PURPOSE:To ensure a reproduction of only the required signal group with a simple demodulator, by giving a different digital modulating system to the signals to be transmitted with every group and then transmitting them with a time-division multiplication given with every group. CONSTITUTION:The signals supplied to the input terminals 11 and 12 are grouped in time division through a multiplying circuit 13. One of the grouped signals is modulated by an FSK modulator 21, and the other one is modulated by a double- phase modulator 22. These modulated signals receive a time-division multiplication through a synthesizing circuit 23 to be turned into a row of signals. At the reception side, the FSK modulated wave is demodulated by a demodulator 24, and the double-phase modulated wave is demodulated by a synchronizing circuit 25. The demodulated signal is applied to a reproducing circuit 26 to reproduce a code, and at the same time selected for only the necessary signal through the circuit 25 to be delivered to a terminal 27.