1. A speech recognition apparatus comprising: a transformation processor configured to transform at least one phoneme sequence included in speech into at least one word sequence, and to provide, for said word sequence, an appearance probability indicating that said phoneme sequence originally represented said word sequence; a renewal processor configured to renew said appearance probability, provided for said word sequence by said transformation processor, based on a renewed numerical value indicated by language models corresponding to said word sequence provided by said transformation processor; and a recognition processor configured to recognize speech by selecting one of said word sequences for which the renewed appearance probability is the highest to indicate that said phoneme sequence originally represented said selected word sequence; wherein said renewal processor calculates said renewed numerical value using a first language model, which is especially prepared for expressions unique to spontaneous speech, and a second language model, which differs from said first language model, and employs said renewed numerical value to renew said appearance probability.