PURPOSE: To make the change of state difficult to be mistaken and in addition, capable of being acknowledged quickly by setting properly the number of times of decision in conformity with the property of a state signal from each monitored object.

CONSTITUTION: This device is provided with a sampling means Bc to sample successively plural signals inputted from the monitored object R, a comparing means Bd1 between a present time state and a last time state, a last time state updating means Bd2 to change the present time state into the last time state, a number of times of decision substituting means Bd3 to read the number of times of decision of the monitored object judged to be different by the comparing means out of a number of times of decision table, and substitute it in a decision count table, an arithmetic means Bd4 to decrease the numerical value of the decision count table of the monitored object the comparing means judges to be the same, a monitored object specifying means Bd5 to specify the monitored object whose numerical value reaches a prescribed value by the decrement of a present time, a present state updating means Bd6 to store the present time state of the monitored object the monitored object specifying means specifies in a present state table and make it the present state, and a number of times of decision registration operating part Be to register the number of times of decision of the number of times of decision table. Besides, a sampling control means and a number of times of pause registration operating part are added.