PURPOSE: To facilitate a correct decision by an operator, by indicating instantly the sequence of the occurrence of an abnormality simultaneously with the lighting of an alarm and by excluding irrelevant alarms from the sequence, when any abnormality occurs in a plant.

CONSTITUTION: When an output value of a detector 11 exceeds a set value 21, a relay 41 is excited, relay contacts 91, 101 and 51 are closed, and an alarm 61 is lighted. Simultaneously a shift register 7 is triggered, the sequence 1, 2... n of the occurrence is outputted and sent to a memory 81 to be stored, and the content of the memory is indicated in an alarm indicating element, while the memory 81 is self-held even when the contacts are turned OFF. Each signal of the memory 81 is inputted in an operating and processing unit constituted by a microprocessor, etc., and irrelevent alarms are excluded from the sequence in comparison with a data base containing the sequence classified into each cause of an abnormality beforehand. By this constitution, a correct decision of an operator is facilitated.