An IO3 that is a connecting node reads waveform data from respective regions, in a TL frame circulated in a first sub-network system, corresponding to transmission channels allocated to any node belonging to the first sub-network system and writes the read waveform data into the regions, in a TL frame circulated in a second sub-network system, corresponding to the same transmission channels, and reads waveform data from regions, in the TL frame circulated in the second sub-network system, corresponding to the transmission channels allocated to any node constituting the second sub-network system and writes the read waveform data into the regions, in the TL frame circulated in the first sub-network system, corresponding to the same transmission channels.