1. A signal enhancement device comprising: spectral subtraction means for subtracting a given reference signal from a main input signal containing a target signal and a noise signal by spectral subtraction; an adaptive filter applied to said reference signal; coefficient control means for controlling a filter coefficient of said adaptive filter in order to reduce the noise signal component in said main input signal; and a database of a signal model concerning said target signal expressing a given feature concerning the target signal by means of a given statistical model, wherein said coefficient control means performs control of said filter coefficient based on a likelihood of said signal model with respect to an output signal from said spectral subtraction means.