Disclosed is a piano sound source apparatus for adding a piano sound source providing a plurality of sinusoidal oscillation frequencies and a noise source providing a plurality of noise oscillation frequencies to output a composite tone. The apparatus includes an oscillation control unit that controls the frequency and amplitude of each of sine waves corresponding to the sinusoidal oscillation frequencies on the basis of time, an amplitude control unit that controls the amplitude of each of the sine waves corresponding to the sinusoidal oscillation frequencies in accordance with the intensity of the composite tone, and a mixing-proportion control unit that controls the amplitude of each of the noise oscillation frequencies in accordance with the intensity of the composite tone to control the mixing proportion of the amplitudes of the noise oscillation frequencies and those of the sine waves corresponding to the sinusoidal oscillation frequencies.