<p>A hearing aid (100) is provided with a body (10) and a battery holder (50) which can be opened from and closed to the body (10) by being rotated about a rotation shaft. The body (10) is provided with a lock bar (12) provided so as to traverse the containing space in which the battery holder (50) is contained, and also with a projection (14) projecting toward the containing space. The battery holder (50) is provided with a first recess (62) and a second recess (64) with which the lock bar and the projection engage.</p>
