1. An information retrieval apparatus comprising: input means for inputting a document; designation means for designating a desired character sequence in the document input by the input means; retrieval means for searching a database on the basis of the character sequence designated by the designation means and acquiring a plurality of retrieval results; sentence cutting-out means for cutting out a sentence associated with the character sequence designated by the designation means, from the document input by the input means; sentence analysis means for analyzing the sentence cut out by the sentence cutting-out means; keyword generating means for generating a keyword from a sentence analysis result acquired by the sentence analysis means; calculation means for calculating an evaluation value of each of the retrieval results obtained by the retrieval means, with use of the keyword generated by the keyword generating means; and selection means for selecting a predetermined one of the retrieval results on the basis of the evaluation values calculated by the calculation means.