1. An information processing apparatus, comprising: a collection unit which collects a document consisting of one or more sentences; a topic analysis unit which calculates a probability indicating a degree of fitness of each sentence constituting the collected document for each item of a local topic by performing topic analysis on the collected document; a language analysis unit which detects a unique expression pattern in each item of the local topic by performing linguistic analysis on the collected document; an evaluation setting unit which sets topic usefulness for each sentence constituting the collected document on the basis of evaluation of the sentence by an evaluator, and sets a total evaluation value with respect to each item of the local topic on the basis of the topic analysis result and the topic usefulness; and a profound text extraction unit which selects an item of the local topic on the basis of the total evaluation values, and extracts appropriate sentences for a unique expression pattern in the selected item of the local topic from the collected document as profound text candidates.