1. An information processing apparatus comprising: category classifying means for classifying a document into one or more categories among a plurality of categories; word extracting means for extracting one or more words from the document; word score calculating means for calculating a word score for each of the one or more words extracted from the document by the word extracting means on the basis of an appearance frequency of the word in each of the one or more categories into which the document is classified by the category classifying means, the word score serving as an index of interest of the word; sentence-for-computation extracting means for extracting one or more sentences from the document; and sentence score calculating means for calculating a sentence score for each of the one or more sentences extracted by the sentence-for-computation extracting means on the basis of the word score calculated by the word score calculating means, the sentence score serving as an index of interest of the sentence.