Subsignal transmitting system

Disclosed is a subsignal transmitting system having working lines (A,B) for respectively transmitting multiplexed signals each including a main signal and having at least one protection line (C) for transmitting one of the multiplexed signals when it is detected that the transmitting conditions of one of the working lines (A,B) along which the signals are being transmitted are deteriorated. To realize the switching of the subsignal transmitting through the protection line (C), the system comprises a switching signal transmission line (D) for transmitting in the direction opposite to the transmission of the multiplexed signals, a switching signal indicating which one of the working lines (A,B) is deteriorated for transmission of the corresponding multiplexed signal, a transmitting side subsignal switching unit (6,9) for outputting one of the input subsignals to one of the working lines (A,B) respectively and for outputting, in response to the switching signal, one of the input subsignals to the protection line (C); and a receiving side subsignal switching unit (13,14), operatively connected to the subsignal output terminals (OS1,OS2) for outputting the subsignal through the protection line (C) to, in response to the switching signal, the corresponding one of the subsignal output terminals (OS1,OS2), the remaining subsignals through the working lines (A,B) being output to the remaining output terminals, respectively.