A hearing aid (100) comprises a main body (10) and a battery holder (50) that can be opened and closed with respect to the main body by revolving around a revolving shaft. The main body (10) has a lock bar (12) provided so as to traverse the space in which the battery holder (50) is installed, and a protruding portion (14) that protrudes toward this installation space. The battery holder (50) has a first concave portion (62) and a second concave portion (64) that latch the lock bar and the protruding portion.
