To provide a hearing aid system which enhances sound and suppresses a noise with respect to the sound and noise monitored from a plurality of directions.

In the hearing aid system which hearing-aid-processes an output signal of microphones 5 and 25 and wears hearing aids 2 and 3 in both ears which convert the hearing-aid-processed signal into sound pressure by earphones 8 and 28 for output, there are processing means 6 and 26 which estimate a sound arriving from each direction set in advance by use of a header transfer function (HRTF) from an output signal of the microphones 5 and 25 of each of the hearing aids 2 and 3, and enhance a sound in which a difference between the right and left in a modulation degree of a low frequency component of an envelope of the estimated sound in each direction is smaller than a given value.