3. A speech recognition apparatus where a system that is an object of analysis is provided with a plurality of states, comprising a code book in which a feature vector space is clustered and representative vectors of respective clusters are stored in a form searchable by labels thereof, a cluster occurrence probability storing means for storing occurrence probabilities of the respective labels in the respective states, a membership degree calculating means for calculating membership degrees of observation vectors to the respective clusters by using the code book and an observation vector occurrence degree calculating means for calculating a product sum of logarithmic values of the calculated membership degrees of the observation vectors to the respective clusters and the occurrence probabilities of the respective clusters stored in the cluster occurrence probability storing means or an amount equivalent thereto and calculating occurrence degrees of the observation vectors in the respective states of the system.
3. A speech recognition apparatus where a system that is an object of analysis is provided with a plurality of states, comprising a code book in which a feature vector space is clustered and representative vectors of respective clusters are stored in a form searchable by labels thereof, a cluster occurrence probability storing means for storing occurrence probabilities of the respective labels in the respective states, a membership degree calculating means for calculating membership degrees of observation vectors to the respective clusters by using the code book and an observation vector occurrence degree calculating means for calculating a product sum of logarithmic values of the calculated membership degrees of the observation vectors to the respective clusters and the occurrence probabilities of the respective clusters stored in the cluster occurrence probability storing means or an amount equivalent thereto and calculating occurrence degrees of the observation vectors in the respective states of the system. 4. The speech recognition apparatus according to claim 3, wherein the cluster occurrence probability storing means in each state stores the occurrence probabilities calculated such that with regard to a predetermined N a total sum of the probabilities becomes 1 with respect to the clusters having higher orders of up to N with regard to the occurrence probabilities and the occurrence probabilities of other of the clusters are rendered 0.