5. An apparatus according to claim 1 , further comprising a search query generating device configured to generate a search query on the basis of a keyword group of one of the topic cluster and the subtopic cluster.
5. An apparatus according to claim 1 , further comprising a search query generating device configured to generate a search query on the basis of a keyword group of one of the topic cluster and the subtopic cluster. 9. An apparatus according to claim 5 , which further comprises a genre estimation device configured to estimate a genre of one of the topic cluster and the subtopic cluster and assign a genre name thereto, and in which the search query generating device switches search query generating methods in accordance with the genre name estimated by the genre estimation device.