A system capable of reducing the influence of sound reverberation or reflection to improve sound-source separation accuracy. An original signal X(ω,f) is separated from an observed signal Y(ω,f) according to a first model and a second model to extract an unknown signal E(ω,f). According to the first model, the original signal X(ω,f) of the current frame f is represented as a combined signal of known signals S(ω,f−m+1) (m=1 to M) that span a certain number M of current and previous frames. This enables extraction of the unknown signal E(ω,f) without changing the window length while reducing the influence of reverberation or reflection of the known signal S(ω,f) on the observed signal Y(ω,f).