A hearing aid (1 2 3 4 5 6 7) comprising: a hearing-aid processing unit (12 22 32 42 52) configured to amplify a first acoustic signal received by a microphone (11 21), according to an ability of a user to hear sound in each of a plurality of frequencies, to produce a second acoustic signal; a predetermined-sound detection unit (13 23 43 53 63 73) configured to detect a predetermined sound included in the first acoustic signal and abruptly occurs, and to produce a control signal, which indicates a generation timing of the predetermined sound; and a predetermined-sound suppression unit (14 24) configured to receive the control signal and to suppress the second acoustic signal, based on the control signal, wherein the hearing-aid processing unit (12 22 32 42 52) includes: a frequency conversion unit configured to produce a spectrum signal which indicates a frequency component included in the first acoustic signal; wherein the hearing aid (1 2 3 4 5 6 7) is configured to detect the predetermined sound included in the first acoustic signal in the predetermined-sound detection unit (13 23 43 53 63 73) in parallel with performing the hearing-aid processing on the first acoustic signal in the hearing-aid processing unit (12 22 32 42 52), characterized in that the hearing aid further includes a gain calculation unit (222 522) configured to calculate a control gain from the spectrum signal produced by the frequency conversion unit; and a gain application unit (225 325) configured to amplify the first acoustic signal using the control gain calculated by the gain calculation unit (222 522) to produce the second acoustic signal, wherein the control gain indicates, for each of the frequencies, an amount of amplification of the first acoustic signal, according to the ability of the user to hear sound in each of the frequencies, and wherein the predetermined-sound detection unit (13 23 43 53 63 73) is configured to detect the predetermined sound included in the first acoustic signal from the spectrum signal. a hearing-aid processing unit (12 22 32 42 52) configured to amplify a first acoustic signal received by a microphone (11 21), according to an ability of a user to hear sound in each of a plurality of frequencies, to produce a second acoustic signal; a predetermined-sound detection unit (13 23 43 53 63 73) configured to detect a predetermined sound included in the first acoustic signal and abruptly occurs, and to produce a control signal, which indicates a generation timing of the predetermined sound; and a predetermined-sound suppression unit (14 24) configured to receive the control signal and to suppress the second acoustic signal, based on the control signal, a frequency conversion unit configured to produce a spectrum signal which indicates a frequency component included in the first acoustic signal; wherein the hearing aid (1 2 3 4 5 6 7) is configured to detect the predetermined sound included in the first acoustic signal in the predetermined-sound detection unit (13 23 43 53 63 73) in parallel with performing the hearing-aid processing on the first acoustic signal in the hearing-aid processing unit (12 22 32 42 52), characterized in that the hearing aid further includes a gain calculation unit (222 522) configured to calculate a control gain from the spectrum signal produced by the frequency conversion unit; and a gain application unit (225 325) configured to amplify the first acoustic signal using the control gain calculated by the gain calculation unit (222 522) to produce the second acoustic signal, wherein the control gain indicates, for each of the frequencies, an amount of amplification of the first acoustic signal, according to the ability of the user to hear sound in each of the frequencies, and wherein the predetermined-sound detection unit (13 23 43 53 63 73) is configured to detect the predetermined sound included in the first acoustic signal from the spectrum signal.