By comprising a question sentence input unit for receiving a question sentence for retrieval, a retrieval execution unit for retrieving data from a database storing data to be retrieved and extracting data similar to the question sentence inputted by the question sentence input unit, a word contribution degree calculation unit for calculating the contribution degree of a word contributing to the extraction by the retrieval execution unit and a word contribution degree output unit for the contribution degree calculated by the word contribution degree calculation unit together with the corresponding word, the word to which importance is attached can be reported to a user.