To reduce possibility that individual data channels are obstructed by separating data of the individual data channels between two wavelength channels.

Data channels are directly connected to a redundant information inserting means and a means for distributing wavelength is directly connected to the redundant information inserting means. A data channel Ch1 includes information units 1 to 6 concerning the time unit of a time 1 to a time 6, which are converted to redundant information units A1 to A8 by a redundant information inserting means. As for a data channel Chn, the units 1 to 6 are also converted to redundant information units X1 to X8. The data A1 to A8 and X1 to X8 are distributed between wavelength channels, and all the information items of the data channel, namely data A1 to A8, are distributed among eight different wavelength channels. Transmission of each first information unit concerning each data A1 to X1 is performed in one wavelength channel.