To provide a digital hearing aid device which can obtain certain hearing aid effect even in case of change of noise environment and suppress unsteady environment noise at the same time when high-sound-quality processing by band expansion is applied to a narrow-band sound signal.

The device has an analog/digital conversion part 11, a band-pass filter part 12 which divides a digital sound signal into a plurality of bands and outputs digital sound signals of the respective bands, a noise level calculation part 13 which calculates the noise levels of the divided bands, an amplification characteristic calculation part 14 which calculates amplification characteristics of the respective bands according to the calculated noise levels, a nonlinear amplification part 15 which suppresses the noise signals of the respective bands and also nonlinearly amplifies the digital sound signals of the respective bands according to the calculated amplification characteristics of the respective bands, an adder 16 which adds and outputs the amplified digital sound signals of the respective bands, and a digital/analog conversion part 17 which converts the addition signal into an analog sound signal.