PURPOSE: To search an abnormal position accurately and promptly from the abnormal state generated in a system by selecting one included in the abnormal data among the basic patterns in accordance with the collation for the abnormal data and each basic pattern.

CONSTITUTION: In the case of power failure accident in an electric power system, for example, the basic patterns 1 are plural basic connecting relations of each element belonging to the power system such as a breaker, transformer, transmission line, etc. Accident data 2 indicate each element in the accident generating range, i.e. power failure section and their connecting relations. A connection rule 3 is fundamentally an experimental rule, and assumed accident data and assumed accident position corresponding thereto are indicated in the IF/THEN form. By an analyzing part 4, one included in the accident data 2 among the basic patterns 1 is selected in accordance with the collation for the basic patterns 1 and accident data 2. Then, the accident position is selected in the collation part 5 based on with the analyzed result from the analyzing part 4, the accident data 2, and the connection rule 3, then outputted.