Mask generation section generates an evaluating mask, indicative of a degree of dissonance with a target sound per each frequency along a frequency axis, by setting, for each of a plurality of peaks in spectra of the target sound, a dissonance function indicative of relationship between a frequency difference from the peak and a degree of dissonance with a component of the peak. Index calculation section collates spectra of an evaluated sound with the evaluating mask to thereby calculate a consonance index value indicative of a degree of consonance or dissonance between the target sound and the evaluated sound.