To decrease the number of communication channels require for the number of communication units in a conventional system and required for communication of supervising the communication units from a supervisory device of a center.

Fault detectors 41, 42, 43 detect fault information from communication units 51, 52, 53, convert the information into information in compliance with the Internet Protocol IP, and transmit the resulting information to a transmitter A 81 by using a wireless LAN. The transmitter A81 transmits the information to a transmitter B71, and the transmitter B71 transmits the information to fault notice devices 21, 22, 23 by using a wireless LAN. The fault notice devices 21, 22, 23 demodulate the fault information into information with the original format and transmit the resulting information to supervisory devices 11, 12, 13.