One surface of a housing is furnished with an opening larger in diameter than a bone conduction device placed therein. A cushioning material is arranged on the inside surface of the opening, and an abutting member secured to a plate yoke constituting the bone conduction device is supported on the cushioning material, such that the top surface thereof is positioned slightly above the surface of the housing. The cushioning material is an annular disk in which is formed a center hole slightly smaller in diameter than the outside diameter of the bone conduction device. The outside peripheral half of the cushioning material is secured resting on the upper edge of the opening of the housing, and the outside edge of the abutting member is secured resting on the upper edge of the center hole of the cushioning material.