Useful knowledge is acquired from a large amount of data by extracting concepts of a unique characteristic. The present invention comprises a concept extractor and a unique concept extractor. The concept extractor extracts categorized concepts from the data. The unique concept extractor is a device for extracting unique concepts from those extracted concepts, and extracts in the categorized concepts, of the concepts belonging to the same category, a concept whose statistical characteristic is distinguished beyond a threshold with respect to the set in which it belongs.