To reduce a refresh time of a large amount of data with respect to all stations regardless of a large scale station configuration.

In the initial processing of a central monitor control station, when an information transmitter is arisen, ON-information is requested to all stations on the restoration of a fault and the information transmitter receiving the ON information request sends only the ON information to the central monitor control station. The central monitor control station stores a station on request to identify and collate a station returning a reply and to receive the ON information and compares it with a state of preceding data to cause a state change from OFF to ON in the case of the OFF state so far, a state of OFF as to other data and a state change from ON to OFF when the state of preceding data denotes ON.