1. A speech recognition apparatus for recognizing a speech, comprising: transformation function storing means for storing at least one transformation function for transforming one of an input speech and an acoustic model used for recognizing the speech when transforming one of the input speech and the acoustic model and adapting the transformed one to the other; allocating means for detecting the best transformation function to adapt the one of the input speech and the acoustic model corresponding to the input speech to the other from at least one transformation function stored in said transformation matrix storing means based on the transforming result of transforming the one of the input speech and the acoustic model by at least one transform function stored in said transform function storing means, and for allocating the input speech to the best transformation function; speech storing means for storing the input speech to which the transformation function is allocated; transformation function updating means for updating the transformation function to which a new input speech is allocated by said allocating means from at least one transformation function stored in said transform function storing means by using all the input speeches allocated to the transformation function; transformation function selecting means for selecting the transformation function used for transforming one of the input speech and the acoustic model from at least one transformation function stored in said transform function storing means; transforming means for transforming one of the input speech and the acoustic model by the transformation function selected by said transformation function selecting means; and matching means for performing matching processing in which the one of the input speech and the acoustic model transformed by the transformation function matches the other and for outputting the result of recognizing the input speech based on the matching processing result.