PURPOSE: To speedily match grasped states on a management device side which detects a change in state and a display device side which displays the state obtained from the management device side.

CONSTITUTION: First and second alarm management devices 41 and 42 are connected to an alarm display device 43 and informs the alarm display device 43 of the occurrence and restoration of information transmission devices 461-465 under the control of them. The respective devices 41-43 calculate numerals intrinsic to the order of a fault in order each time the fault occurs, and hold those results. When the fault is remedied, numerals having the opposite polarity are calculated. The alarm display device 43 collates its numeral with the numerals on the sides of the alarm management devices 41 and 42 at specific timing and resends the state of the fault unless they match each other.