<p>A through hole (102) is formed to penetrate a substrate (101) from its upper surface to its lower surface. The substrate (101) has a vibration electrode film (103) formed so as to cover the through hole (102). The vibration electrode film (103) at the portion on the through hole (102) functions as a diaphragm (104). The through hole (102) on the upper surface of the substrate (101) has a hexagonal opening.</p>
