A first filter (2061 in FIG. 1) calculates a long-time average of first change quantities based on a difference between a line spectral frequency of an input voice signal and a long-time average thereof. A second filter (2062 in FIG. 1) calculates a long-time average of second change quantities based on a difference between a whole band energy of the input voice signal and a long-time average thereof. A third filter (2063 in FIG. 1) calculates a long-time average of third change quantities based on a difference between a low band energy of the input voice signal and a long-time average thereof. A fourth filter (2064 in FIG. 1) calculates a long-time average of fourth change quantities based on a difference between a zero cross number of the input voice signal and a long-time average thereof. A voice/non-voice determining circuit (1040 in FIG. 1) discriminates a voice section from a non-voice section in the voice signal using the long-time average of the above-described first change quantities, the long-time average of the above-described second change quantities, the long-time average of the above-described third change quantities, and the long-time average of the above-described fourth change quantities.