There are provided multiple candidates for FEC codes selectable for each of the ONTs. An OLT is provided with: means for storing redundancy and a code length of each FEC code in a table; means for selecting an FEC code; means for encoding or decoding data using the selected FEC code; means for calculating a bandwidth in consideration for the FEC redundancy and the code length with reference to the table during band assignment calculation; and means for notifying the destination ONT of the selected FEC code.