2. A speech recognition system according to claim 1 , further comprising: a third determiner for determining whether a first prior word information of the prior N pieces of word information agrees with a first posterior word of the posterior N pieces of word information, the first prior word information corresponding to the utterance data having a highest value within data relative to the prior N pieces of word information, the first posterior word information corresponding to the utterance data having a highest value within data relative to the posterior N pieces of word information.
3. A speech recognition system according to claim 2 , further comprising: a replacer for replacing the first prior word information of the prior N pieces of word information with the first posterior word of the posterior N pieces of word information in the case that the first prior and posterior vocabularies information disagree.