Abstract: The present invention relates to a demodulation method for enhancing decoding performance of information bits in a constant-amplitude multi-code biorthogonal modulation communication system, which performs encoding to cause the level of a transmission symbol to be constant. In the demodulation method of the present invention, a demodulator demodulates the received signal, the demodulator having four blocks. C (c?2k, k is the number of information bits) bit streams with higher correlation values in descending order are selected and combined among demodulated bit streams to establish c4 bit stream candidates. A parity check is performed with respect to the c4 bit stream candidates, a candidate group having a maximal sum of correlation values is selected among candidate groups in which any error is not generated at the parity check. A bit stream corresponding to the selected candidate group is determined to be an output of a receiver.