PLANT OPERATION ASSISTANCE DEVICE AND OPERATION ASSISTANCE METHOD

The purpose of the present invention is to quickly stop a plant when an abnormality occurs so as to avoid an increase in damage cost due to propagation of the abnormality. An operation assistance device 200 comprises: a diagnosis means 500 for diagnosing an operation state of a plant 100 on the basis of operation data 3; an abnormality propagation prediction means 600 for predicting, on the basis of the diagnosis results obtained by the diagnosis means 500 and by using a physical model, the devices to which the abnormality will propagate and the time thereof; a cost calculation means 700 for predicting, on the basis of the results of the abnormality propagation prediction means 600, the change over time of the damage cost; and a plant stop determination means 800 for generating a signal that stops the plant 100 if the damage cost is equal to or greater than a predetermined damage cost of suddenly stopping the plant 100.