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, wherein the profound text states knowledge about an attention target by indicating the document that states the local topic relating to the attention target with the unique expression pattern, and sentences of which a degree of profundity is equal to or greater than a predetermined threshold value are recognized as profound text, and wherein the collection unit, the topic analysis unit, the language analysis unit, the evaluation setting unit, and the profound text extraction unit are each implemented via at least one processor.