A hearing aid used for a low tone frequency band, a hearing aid used for a high tone frequency band, and a controller that compares sound pressure of the high tone frequency band split by a frequency band analyzer of the hearing aid used for the high tone frequency band with sound pressure of the high tone frequency band split by a frequency band analyzer of the hearing aid used for the low tone frequency band. If the sound pressure of the high tone frequency band of the hearing aid used for the low tone frequency band is higher by at least a specific amount than the sound pressure of the high tone frequency band of the hearing aid used for the high tone frequency band, the sound pressure of the high tone frequency band of the hearing aid used for the high tone frequency band is raised.