To eliminate the possibility of the current leakage to an object to be vibrated and to enhance electrical safety by constituting an output member and lining member of an insulating material.

A diaphragm 2 is held between a columnar output block (output member) 4 and a lining block (lining member) 6. The output block 4 and the lining block 6 may be formed not only to the columnar shape but to suitable shapes as well. The output block 4 and the lining block 6 are composed of an insulating material. For example, glass, etc., are used as the insulating material. The glass is more preferable as the glass is the insulating material having the relatively high fracture threshold and easy availability. The insulating material is not limited to glass and ceramics, single crystals of metal oxides, silicon single crystals, diamond, etc., are preferable as these insulating materials having the high fracture threshold. Since the output block 4 and the lining block 6 are insulators, the leakage of the electric signal to be impressed to the diaphragm 2 to other matters does not occur and the electrical safety may be assured.