A coding section 101 performs error detection coding of data for each predetermined error detection unit, and an M-ary modulation section 102 arranges data belonging to a plurality of error detection units in one transmission unit, and transmits that data. A first decoding section 114 decodes a received signal, and performs error detection on the decoding result for each error detection unit. A second demodulation section 115 modifies the likelihood of each bit based on the result of error detection in the first decoding section 114. By this means, it is possible to improve the error correction capability of a signal that has undergone M-ary modulation using high-precision likelihoods, and to improve transmission quality.