An FEC frame structuring device includes a multi-lane distributing unit that distributes a data frame to be transmitted to n lanes, FEC coding units each performs FEC coding of the distributed data frame independently for each of the n lanes to generate an FEC frame, a multiplexing unit that multiplexes the FEC frame from the FEC coding units by relating to m channels of an optical signal, a demultiplexing unit that demultiplexes the m channels of the received optical signal by relating to the n lanes, FEC decoding units each performs FEC decoding of the demultiplexed FEC frame independently for each of the n lanes, and a multi-lane synchronizing unit that synchronizes the n lanes with each other after the FEC decoding performed by the FEC decoding units to reconstruct the original data frame.