1. A speech recognition apparatus for calculating a degree of likelihood of a non-language speech from an unidentified input speech, said speech recognition apparatus calculating, per path, a cumulative score of a language score, a word acoustic score and a garbage acoustic score and outputting a word string with a highest cumulative score as a recognition result of the unidentified input speech including a non-language speech, said apparatus comprising: a garbage acoustic model storage unit operable to store, in advance, a garbage acoustic model which is an acoustic model learned from a collection of a plurality of unnecessary words; a feature value calculation unit operable to calculate a feature parameter necessary for recognition by acoustically analyzing the unidentified input speech per frame which is a unit for speech analysis; a garbage acoustic score calculation unit operable to calculate the garbage acoustic score by comparing the feature parameter and the garbage acoustic model per frame; an estimate value calculation unit operable to calculate, per frame, an estimate value which indicates a degree of likelihood to be a non-language speech of one of the plurality of unnecessary words; a garbage acoustic score correction unit operable to correct the garbage acoustic score calculated by said garbage acoustic score calculation unit so as to raise the score only in the frame where the non-language speech is inputted by adding the estimate value to the garbage acoustic score, the estimate value being calculated by said estimate value calculation unit, and the garbage acoustic score being calculated by said garbage acoustic score calculation unit; and a recognition result output unit operable to output the word string as the recognition result of the unidentified input speech, the word string having the highest cumulative score of the language score, the word acoustic score, and the garbage acoustic score corrected by said garbage acoustic score correction unit.
2. The speech recognition apparatus according to claim 1 , wherein said estimate value calculation unit includes a non-language speech estimation unit operable to calculate, per frame, an estimate value which indicates a degree of likelihood to be a non-language speech of one of the plurality of unnecessary words, using a non-language speech estimate function, and said garbage acoustic score correction unit corrects the garbage acoustic score so as to raise the score by using the estimate value calculated by said non-language speech estimation unit in the frame where the non-language speech is inputted.