A pole piece 19 of a speaker main unit 1 has a pole 19a engaged with a bobbin 14 from the back side of a diaphragm 12, and a flange 19b horizontally expanding from the base of the pole 19a. In the pole 19a is formed a through hole 19c passing therethrough in an axial direction thereof, and in the bottom end of the through hole 19c is provided with a taper 19d which widens with it goes downward. A thin film piezoelectric element 4 is provided such that the element covers an external opening 19e of the through hole 19c, and one end 4a of a thin film piezoelectric element 4 is adhered to the bottom surface of the flange 19b.