PROBLEM TO BE SOLVED: To extract a complaint directly useful for improvement of an evaluation object product out of a document written by a user of the evaluation object product.SOLUTION: A positive evaluation expression identifying unit 104 identifies a sentence (a first sentence) including an expression conveying a positive evaluation on a comparative object out of a collection of sentences stored in a sentence collection acquiring unit 101. A negative evaluation expression identifying unit 105 identifies an evaluation object and an expression conveying a negative evaluation corresponding to the positive evaluation out of the first sentence or a sentence before or after the first sentence (a second sentence). A complaint sentence extracting unit 106 extracts as a complaint sentence: the first sentence including a positive evaluation, or an evaluation object and a negative expression; or consecutive two sentences constituted by the first sentence including a positive evaluation, and the second sentence including an evaluation object and a negative evaluation. In a contrast expression including a positive evaluation of a comparative object and a negative evaluation of an evaluation object implicitly shows an absolute evaluation based on a user's criterion. A developer of the product accesses a complaint storing unit 107 and refers to the complaint, to thereby perform immediate feedback to improvement of the product.
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