A category pair is generated in a round-robin fashion for all of categories by obtaining each category of a document directory, each category of a bookmark, and a URL registered to each category from each of a document directory storing unit and a bookmark storing unit, and the degree of similarity is calculated for each category pair. Next, a pair of categories whose degrees of association are high is selected from among all of category pairs, and a URL candidate to be recommended each other is extracted for each selected category pair.