To easily specify a disconnection part inside a tunnel by an operation, on the side of a disaster prevention reception panel.

For the tunnel disaster prevention facilities, terminal equipment, such as a detector 5 and control equipment installed inside the tunnel, is connected to a transmission line 2a comprising a power line and a signal line pulled out from the disaster prevention reception panel 1, a relay amplification panel 7 is connected at prescribed intervals, the respective relay amplification panels 7 supply power to an outgoing side transmission line at a terminal side and the inside of the tunnel is monitored and controlled. The relay amplifying panel 7 is provided with a backup circuit for backing up power supply to a disconnected incoming side transmission line and signal transmission with the disaster prevention reception panel, at detecting of the disconnection of the incoming side transmission line at the side of the disaster prevention reception panel 1. The disaster prevention reception panel 1 is provided with a fault investigation part 25 for transmitting the control signals of a fault investigation to the relay amplification panel to temporarily cancel a backup operation for the disconnection of the transmission line, and specifying the disconnection part, on the basis of the response state of the terminal equipment during the time in between.