1. A recognition apparatus for recognizing speech data, comprising: a state transition model for the unknown word, represented by the number of the states and the transition probability among the states; acquisition means for acquiring a state of the maximum likelihood at each time of the speech data, among the plural states employed in the state transition model for the known word, to be employed in the speech recognition of the known word; output means for acquiring the likelihood of a state transition model, obtained by applying the state acquired by said acquisition means to said state transition model for the unknown word, to said speech data, and outputting said likelihood as the transition model of the unknown word and the likelihood therefor; and recognition means for effecting recognition of said speech data, based on the likelihood obtained with said state transition model for the known word and on the state transition model and the likelihood for the unknown word.