A disclosed signal transmission method in a radio multiplex transmission system comprises the steps of: serial-to-parallel converting serial data to be transmitted into N (N: two or more) parallel data series; independently performing an error-correcting encoding process on the parallel signals of the N data series serial-to-parallel converted; parallel-to-serial converting the parallel signals encoded with error-correcting codes; performing an interleaving process on the parallel-to-serial converted signals; serial-to-parallel converting the interleaved signals into L (L: two or more) parallel data series and transmitting each of the L data series using L antennas; receiving the transmitted signals; separating the received signals into M (M: two or more) data series and parallel-to-serial converting the M data series; performing a deinterleaving process on the parallel-to-serial converted signals; serial-to-parallel converting the deinterleaved signals into N data series; independently performing an error-correcting decoding process on the parallel signals of the N data series serial-to-parallel converted; and parallel-to-serial converting the signals in which the error-correcting codes are decoded, thereby recovering the transmitted data.