16. The Hidden Markov Model generation system according to claim 11 , wherein the filler model generation section obtains a cluster value of each of the clusters based on a mean for defining one or a plurality of probability density functions classified in each of the clusters, and obtains a mean for defining probability density functions composing the Hidden Markov Model to be used as the filler model or its state based on the obtained cluster value, and obtains a variance for defining probability density functions composing the Hidden Markov Model to be used as the filler model or its state based on a variance for defining one or a plurality of probability density functions classified into each of the clusters.
11. A Hidden Markov Model generation system that generates Hidden Markov Models to be used for speech recognition with a given speech recognition system, the Hidden Markov Model generation system comprising: a scheduled-to-be used model group storage section that stores a scheduled-to-be-used model group including a plurality of Hidden Markov Models scheduled to be used by the given speech recognition system; and a filler model generation section that generates Hidden Markov Models to be used as filler models by the given speech recognition system based on all or at least a part of the Hidden Markov Model group in the scheduled-to-be-used model group; wherein the filler model generation section classifies a plurality of probability density functions composing all or at least a part of the Hidden Markov Model group in the scheduled-to-be-used model group into a plurality of clusters, obtains a given parameter for defining probability density functions composing Hidden Markov Models to be used as filler models.