To provide an orthogonal frequency-division multiplex modulating and demodulating circuit, which can multiplex and transmit signals differing in bit rate and QoS with a single OFDM line.

Input signals are converted by serial-parallel converters 101, 102, and 103 into a complex parallel signal, and subcarriers and modulation systems are allocated by communication channels. The signal has its arrangement changed by a randomizer 104 and is processed by a discrete Fourier transformer 105 and converted by a parallel-serial converter 106 into a serial signal, which is processed through the orthogonal modulation of a transmitter 107 and outputted from an antenna 115. The signal received by an antenna 116 is processed by the orthogonal demodulation of a receiver 108 and is converted by a serial-parallel converter 109 into parallel signals, which are processed by a discrete Fourier transformer 110 and returned in the order of the original subcarriers by a randomizer 104, so that they are decoded by parallel-serial converters 112, 113, and 114 and outputted.