When judging, for each preset section, whether an input signal is voice or other than voice, a single algorithm is used for judging even when a plurality of kinds of input signal frequency band and section length are available. A unit length division circuit (20) divides a signal from an input terminal (10) into unit lengths (e.g., 2.5 msec) shorter than a frame length (e.g., 10 msec) for transfer to a band conversion circuit (30). The band conversion circuit (30) restricts a frequency band provided by an input signal having a frame length given by the unit length division circuit (20) to a frequency band that can be detected by a detection circuit (40) for transfer to the detection circuit (40). The detection circuit (40) judges whether an input signal on a frame basis from the unit length division circuit (20) falls in a voice section or a voiceless section and transfers the judging result to a unit length conversion circuit (50). The unit length conversion circuit (50) determines the judging result of a frame from a plurality of judging results, corresponding to respective frames, from the detection circuit (40) for outputting from an output terminal (60).