[en] When a alarm is happened in nuclear power plant, operator tries to identify the direct and specific causes of the alarm and to do proper actions to mitigate the effect of it. To recognize the specific causes of it, the operator uses his experiences, alarm procedures, logic diagrams and so on. But, if the alarm procedure described many causes of the alarm unfortunately, it is very difficult for the operator who has no experience on the alarm to search the causes of it in hundreds of logic diagrams when emergency. The proposed system, ACTS(Alarm-Cause Tracking System), tracks and displays the causes of alarms on-line from computerized logic diagrams. And the system highlights the specific procedures related the causes in the procedure of the alarm