PURPOSE: To eliminate the need for a cover covering a coaxial switching device not in use and a change in a switch in the case of the extension of a transmitter by providing a means sending connection information to the coaxial switching device.

CONSTITUTION: N sets of active transmitters 11-1N and one standby transmitter 2 are provided on the system and N-sets of coaxial switching devices 31-3N are used to replace one of the active transmitters with the standby transmitter 2 and to connect the standby transmitter 2 to antennas 41-4N and a control section 5 and the standby transmitter or the active transmitters are connected to a dummy load 6. Moreover, the control section 5 controls the coaxial switching devices 31-3N and the transmitters 11-1N and 2 and displays the connecting state of the coaxial switching devices. When the coaxial switching devices 31-3N are connected to the control section 5 so as to be in use, the information represending it is fed to the control section 5 through terminal pairs short-circuited to each other and the control section 5 is provided with a circuit lighting up one of plural display devices implementing the switching display of the active and standby equipments from the unconnected coaxial switching devices.