Abstract: When external pressure extremely increases, a waterproof vibration membrane tends to be resiliently deformed extremely toward the inside. However, an inward resilient deformation inhibiting member provided on the inner side of the waterproof vibration membrane with a space therebetween inhibits this extreme inward resilient deformation of the waterproof vibration membrane, whereby the waterproof vibration membrane is prevented from being ruptured or plastically deformed. On the other hand, when the internal pressure extremely increases, the waterproof vibration membrane tends to be resiliently deformed extremely toward the outside. However, an outward resilient deformation inhibiting member provided on the outer side of the waterproof vibration membrane with a space therebetween inhibits this extreme outward resilient deformation of the waterproof vibration membrane, whereby the waterproof vibration membrane is prevented from being ruptured or plastically deformed.