A communication network system comprising: a first transmission channel; a second transmission channel different from the first transmission channel; a first device connected to the first transmission channel and not connected to the second transmission channel; a second device connected to the second transmission channel and not connected to the first transmission channel; and a third device electrically connecting the first transmission channel and the second transmission channel, the third device not transmitting a short-circuit state occurring in one of the first transmission channel and the second transmission channel to a transmission channel other than the one of the first transmission channel and the second transmission channel, the communication network system further comprising: a plurality of the second transmission channels (60a to 60e); a plurality of the second devices (20aa to 20ef); and a plurality of the third devices (10, 10a to 10e), wherein each of the plurality of the third devices (10, 10a to 10e) electrically connects the first transmission channel and one of the plurality of the second transmission channels, each of the plurality of the third devices (10, 10a to 10e) does not transmit a short-circuit state occurring in one of the first transmission channel and the plurality of the second transmission channels to a transmission channel other than the one of the first transmission channel and the plurality of the second transmission channels; wherein each of the plurality of third devices includes an impedance component (13, 14, 19), and wherein the impedance component (13, 14, 19) has an impedance larger than a characteristic impedance of the first transmission channel at a frequency of a signal transmitted by the first transmission channel. a first transmission channel; a second transmission channel different from the first transmission channel; a first device connected to the first transmission channel and not connected to the second transmission channel; a second device connected to the second transmission channel and not connected to the first transmission channel; and a third device electrically connecting the first transmission channel and the second transmission channel, the third device not transmitting a short-circuit state occurring in one of the first transmission channel and the second transmission channel to a transmission channel other than the one of the first transmission channel and the second transmission channel, a plurality of the second transmission channels (60a to 60e); a plurality of the second devices (20aa to 20ef); and a plurality of the third devices (10, 10a to 10e), wherein each of the plurality of the third devices (10, 10a to 10e) electrically connects the first transmission channel and one of the plurality of the second transmission channels, each of the plurality of the third devices (10, 10a to 10e) does not transmit a short-circuit state occurring in one of the first transmission channel and the plurality of the second transmission channels to a transmission channel other than the one of the first transmission channel and the plurality of the second transmission channels; wherein each of the plurality of third devices includes an impedance component (13, 14, 19), and wherein the impedance component (13, 14, 19) has an impedance larger than a characteristic impedance of the first transmission channel at a frequency of a signal transmitted by the first transmission channel.