1 ) a method of calculating an hmm output probability, in which a feature vector obtained by speech analysis of an input speech is vector quantized using vector quantization means and a state output probability in accordance with a result of quantization is obtained by referring to tables, wherein the vector quantization means used for vector quantization are vector quantization means associated with respective subword, and the tables are provided in association with the vector quantization means associated with the subwords, and the feature vector obtained by speech analysis of the input speech is vector quantized using one of the vector quantization means associated with subwords, a result of quantization is output, and a state output probability in accordance with the result of quantization is obtained by referring to a table associated with the vector quantization means that has output the result of quantization: