PURPOSE: To obtain an acoustic device to emit or reclaim a sound with good efficiency underwater by covering a vibrating part to emit or reclaim the sound with a covering material having a water-proof character and, simultaneously, a flexibility.

CONSTITUTION: A vibrating part 20 is composed of a diaphragm 21 and a piezo- element 22 coupled to the diaphragm 21, and for a covering material 30 to cover the vibrating part 20, an urethane rubber having the water-proof character and flexibility is adopted. As a means for covering, the means to cover the vibrating part 20 in a thin film condition such as an electrostatic coating and a dipping is adopted. Thus, the vibrating part 20 main body covered with the covering material 30 is directly put under the water, and the sound can be emitted or reclaimed with a good efficiency regardless of a water pressure environment.