PURPOSE: To evade decoding of an erroneous signal by separating the operation result of a word train and a discrimination code superposed in the transmission side from each other and establishing the synchronism of a received and demodulated signal train by a generated syndrome.

CONSTITUTION: An error correction encoder in the transmission side is provided with a means (discrimination code superposer 15) which superposes a specific code on redundant bits generated at the time of error correction encoding of at least one digital input signal train. An error correction decoder in the reception side is provided with a means (discrimination code separator 28) which separates a code determined by the code superposed by the error correction encoder at the time of generating the syndrome by the operation of the word train of the signal train encoded by the error correction encoder. The syndrome is detected by the separating means 28, and the synchronism is established by the detected syndrome. That is, a specific code signal train of the error correction encoder in the transmission side is arbitrarily set, and the word synchronism is established to decode the signal train only when it coincides with the code signal train of the error correction decoder in the reception side.