1. A voice/music judging apparatus comprising: a voice/music judgment feature parameter calculating module configured to calculate values of various feature parameters to be used for discriminating between a voice signal and a musical signal from an input audio signal; a music/background sound judgment feature parameter calculating module configured to similarly calculate values of various feature parameters to be used for discriminating between a musical signal and a background-sound-superimposed voice signal from the input audio signal; a voice/music characteristic score calculating module configured to calculate a score indicating a likelihood that the input audio signal is a voice signal or a musical signal by multiplying the characteristic parameter values calculated by the voice/music judgment feature parameter calculating module by respective weights that were calculated in advance on the basis of learned parameter values of voice/music reference data and adding up weight-multiplied characteristic parameter values; a music/background sound characteristic score calculating module configured to calculate a score indicating a likelihood that the input audio signal is a musical signal or a background-sound-superimposed voice signal by multiplying the characteristic parameter values calculated by the music/background sound judgment feature parameter calculating module by respective weights that were calculated in advance on the basis of learned parameter values of music/background sound reference data and adding up weight-multiplied characteristic parameter values; and a voice/music judging module configured to judge whether the input audio signal is a voice signal or a musical signal on the basis of the score calculated by the voice/music signal characteristic score calculating module and, if it is judged a musical signal, to judge whether the input audio signal is a background-sound-superimposed voice signal or not on the basis of the score calculated by the music/background sound characteristic score.