The voice quality conversion apparatus includes: low-frequency harmonic level calculating units and a harmonic level mixing unit for calculating a low-frequency sound source spectrum by mixing a level of a harmonic of an input sound source waveform and a level of a harmonic of a target sound source waveform at a predetermined conversion ratio for each order of harmonics including fundamental, in a frequency range equal to or lower than a boundary frequency; a high-frequency spectral envelope mixing unit that calculates a high-frequency sound source spectrum by mixing the input sound source spectrum and the target sound source spectrum at the predetermined conversion ratio in a frequency range larger than the boundary frequency; and a spectrum combining unit that combines the low-frequency sound source spectrum with the high-frequency sound source spectrum at the boundary frequency to generate a sound source spectrum for an entire frequency range.