1. An acoustic signal processing apparatus for detecting a featuring portion in acoustic signals, comprising: amplitude calculating means for calculating short-term amplitudes, at an interval of a preset time length in the acoustic signals; candidate domain extraction means for extracting candidate domains of said featuring portion based on said short-term amplitudes; feature extraction means for extracting sound quality featuring quantities, quantifying the sound quality, at an interval of said preset time length in the acoustic signals; and candidate domain evaluating means for evaluating, based on said short-term amplitudes and said sound quality featuring quantities, whether or not said candidate domain is said featuring portion.