4. The speech recognition system according to claim 3 , wherein the judgment reference change processing part judges the utterance speed of the speech data based on the recognition time in speech recognition of the speech data and the number of vowels in an acoustic model of the registered word.
5. The speech recognition system according to claim 4 , wherein the reliability judgment part obtains the likelihood difference between the first registered word and a second registered word whose likelihood is at the second rank, and judges the reliability of the speech data being the first registered word based on the result of comparison between the likelihood difference and the likelihood difference judgment threshold.