6. The topic transition analysis system according to claim 5 , further comprising: a speech recognition unit generating a text string from a speech signal included in the primary media stream, wherein said at least one of the topic similarity calculation unit calculates a topic similarity between the statement and a text string generated by the speech recognition unit from the entire section or an arbitrary section of the media stream which is a similarity calculation target.
5. The topic transition analysis system according to claim 4 , wherein said at least one of the topic similarity calculation unit receives the statement and one or a plurality of statement groups which are similarity calculation targets, calculates document vectors with respect to the statement and the statement groups by adding weight to each term included in the statement and the statement groups based on a given algorithm, calculating distances among these document vectors, and calculating topic similarities based on the distances.