There is provided a behind-the-ear hearing aid that makes it easy for a hearing aid wearer to estimate a position of a sound source with respect to a front-back direction and that enables an increase in aesthetic property when the hearing aid is worn. A behind-the-ear hearing aid of the present invention is used while fitted to an ear of a human body, and includes at least a microphone 101 which collects ambient sound, thereby generating an input signal and signal processing unit 102 that generates an output signal from the input signal. The hearing aid also has a behind-the-ear portion 110 that can be fitted to the ear and a receiver 103 that reproduces output sound from the output signal. When the behind-the-ear portion 110 is fitted to the ear, the microphone 101 is arranged in an entrance of an ear canal that lies in the extension of an ear canal 220 and that is disposed closer to an eardrum than to a plane that is defined by a helix 901, a tragus 902, and an earlobe 903.