PURPOSE: To prevent the degradation of a reception signal due to the degradation of a reception condition by modulating encoding signals which are different in error correction capacity according to the priority of input signals on the transmission side and transmitting the signals, and separating reception signals and decoding the signals after the encoding signals are demodulated on the reception side.

CONSTITUTION: When priority is higher in order input signals 1 to 3 to the transmission side, RS code circuits 101 to 103 in order of higher error correction capacity according to this priority perform an error correction encoding for each signal. These signals are subjected to time-division multiplexing by a multiplexer 104 and to a four-phase phase modulation by a QPSK modulation circuit 105, and are transmitted as transmission signals through a transmission line. On the reception side, a QPSK demodulation circuit 106 demodulates the reception signals and a demultiplexer 107 divides the signals, corresponding to the signals 1 to 3. Next, RS decoding circuits 108 to 110 output signals 1 to 3 which are corresponded to the signals 1 to 3 and for which error decodings are performed. Thus, even if a reception C/N is degradated, the rapid quality degradation of the reception signals can be prevented and the circuitry of a transmitter-receiver can be simplified.