1. A keyword presentation apparatus comprising: a first extraction unit configured to extract, as basic term candidates, morpheme strings, which are defined in a predetermined general concept dictionary, from a document set; a second extraction unit configured to extract, as technical terms, morpheme strings, which are not defined in the general concept dictionary, from the document set; a first selection unit configured to evaluate relevancies between each of the basic term candidates and the technical terms, and to preferentially select basic term candidates having high relevancies as basic terms; a clustering unit configured to calculate weighted sums of statistical degrees of correlation between the basic terms based on the document set, to calculate conceptual degrees of correlation between the basic terms based on the general concept dictionary, and to cluster the basic terms based on the weighted sums; a second selection unit configured to select keywords of respective clusters from the basic terms and the technical terms based on a clustering result of the basic terms; and a presentation unit configured to present selected keywords.