PURPOSE: To take a speedy countermeasure in response to an abnormality signal by automatically judging whether the abnormality signal received from a guard terminal device is effective or not. ;CONSTITUTION: A central processing part 12 once receiving the abnormality signal from a signal reception part 11 judges whether or not the guard terminal device which outputs the abnormality signal is in a guard period from a guard period set by a terminal device guard period setting part 13 and timer data from a timer 14. The central processing part 12 when judging that the guard terminal device is in the guard period displays the signal on an in-guard signal display part 15, but when it is judged that the guard terminal device is not in the guard period, the signal is displayed on a non-guard period signal display part 16.;COPYRIGHT: (C)1993,JPO&Japio
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