A hearing aid according to an embodiment includes a hardware module, a case, and a receiver module. The hardware module is configured to control the hearing aid. The case has an open side and an internal space for accommodating the hardware module. The receiver module is united with the case to form an integrated structure. The receiver module includes a receiver connector fixedly connected at one side thereof with the case, and a receiver formed at the other side of the receiver connector. The hearing aid may further include a case interface unit fixedly formed at a closed side of the case. The hearing aids according to other embodiments are also disclosed.