A chord estimation apparatus includes: frequency-component extraction means for extracting a frequency component from an input music signal; scale-component information generation means for mapping the frequency component extracted by the frequency-component extraction means onto each tone and generating scale-component information including each tone and loudness thereof; folding means for folding the scale-component information generated by the scale-component information generation means for each two octaves to generate scale-component information including 24 tones; and chord estimation means for inputting the scale-component information including 24 tones into a Bayesian network in order to estimate a chord.