1. A speech recognition device comprising: a coefficient storage unit which stores a suppression coefficient representing an amount of noise suppression and an adaptation coefficient representing an amount of adaptation which is generated on the basis of a predetermined noise and is synthesized to a clean acoustic model generated on the basis of a voice which does not include noise, in a manner to relate the suppression coefficient with the adaptation coefficient to each other; a noise estimation unit which estimates noise from an input signal; a noise suppression unit which suppresses a portion of the noise specified by a suppression amount specified on the basis of the suppression coefficient, among from the noise estimated by said noise estimation unit, from the input signal; an acoustic model adaptation unit which generates an adapted acoustic model which is noise-adapted, by synthesizing the noise model, which is generated on the basis of the noise estimated by said noise estimation unit in accordance with an amount of adaptation specified on the basis of the adaptation coefficient, to the clean acoustic model; and a search unit which recognizes voice on the basis of the input suppressed noise by said noise suppression unit and the adapted acoustic model generated by said acoustic model adaptation unit.