PURPOSE: To shorten the transmission time of a signal and to omit a logic required to decide a transmission destination equipment at every transmission of the signal by controlling a duplicated maintenance operation controller by connecting a switch circuit.

CONSTITUTION: When the signals from the maintenance operation controllers 103 and 104 are received at a centralized controller 101, a reception processing is started up, and a received signal is analyzed according to a constant format. Next, it is judged whether or not the maintenance operation controller connected to the switch circuit 102 at present is the one of a waiting system. And when it is the one of the waiting system, the switch circuit 102 is switched. Meanwhile, in case of transmitting the signal from the centralized controller 101, a transmission processing is started up. In the case, the centralized controller 101 edits the signal according to a transmission format, and sends it to a signal line for communication.