A speech recognition device for performing frame synchronization beam search by using a language model score lookahead value prevents the pruning of a correct answer hypothesis while suppressing an increase in the number of hypotheses. A language model score lookahead value imparting device (108) is provided with a word dictionary (203) which defines a phoneme string of a word, a language model (202) which imparts the score of the appearance easiness of a word, and a smoothing language model score lookahead value calculating means (201). The smoothing language model score lookahead value calculating means (201) obtains a language model score lookahead value at each phoneme in the word from the phoneme string of the word defined by the word dictionary (203) and the language model score defined by the language model (202) so that the language model score lookahead values are prevented from concentrating on the beginning of the word.
Language model score lookahead value imparting device and method for the same