1. A keyword presentation apparatus comprising: a first extraction unit, which when executed by a computer, is 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, which when executed by the computer, is 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, which when executed by the computer, is 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, which when executed by the computer, is configured to calculate statistical correlation degrees between the basic terms based on the document set, to calculate conceptual correlation degrees between the basic terms based on the general concept dictionary, and to cluster the basic terms based on weighted sums of the statistical correlation degrees and the conceptual correlation degrees; a second selection unit, which when executed by the computer, is 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, which when executed by the computer, is configured to present the selected keywords on a display device.