A recognition result extraction unit and an agreement determination unit are provided. The recognition result extraction unit extracts, from a recognition result storage unit, N best solutions A and B obtained by an utterance B. The utterance B follows an utterance A corresponding to the N best solutions A and made by a speaker b who is different from a speaker of the utterance A. In a case where a repeat utterance determination unit determines that the N best solutions B are N best solutions obtained by a repeat utterance B according to the utterance A corresponding to the N best solutions A, when the best solution A and B are different each other, the agreement determination unit determines that some or all of the N best solutions A can be replaced with some or all of the N best solutions B.