To provide an ear-hooked hearing aid in which liquid such as water and sweat hardly infiltrates into a battery housing chamber even if the liquid has infiltrated from a gap defined by a case and a battery holder.

Provided is an ear-hooked hearing aid 1 comprising a battery holder 7 which is freely openable and closable. Grooves 9 and 10 are provided on respective edge portions 7a and 7b of the battery holder 7 respectively facing left and right inner surfaces 2a and 2b of a case 2. When the battery holder 7 is in a closed state, cavities 12 and 13 are defined by the grooves 9 and 10 and the left and right inner surfaces 2a and 2b on the case 2, respectively. Further, communication holes 16 and 17 may be provided to make the cavities 12 and 13 communicate to the outside.