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. 7. An apparatus according to claim 5 , which further comprises a device configured to structurize keywords by classifying or hierarchizing keyword groups of the topic cluster and the subtopic cluster, and in which the search query generating device generates a search query by combining a plurality of keywords by using a structurization result of the keywords.