Abstract: In an optical transmitter (10a), an error correction and coding unit (11) performs error correction and coding on data. A framer unit (13) adds header information to n pieces of error-corrected and coded data to generate a frame signal (Fm). A frame dividing unit (14) divides the data of the frame signal into n pieces D1 to Dn, adds the header information to head of each of the n pieces of divided data, and generates n frame signals obtained by adding different CRC values to end. Optical transmission units (5t1 to 5tn) convert the n frame signals into optical signals of different wavelengths and transmit them to n optical transmission paths (17a to 17n). Optical reception units (9r1 to 9rn) of an optical receiver (10b) receive n optical signals and convert them into n frame signals of electrical signals. A frame synthesizing unit (20) determines whether at least one of the n frame signals has an correct CRC value without an error.