A diaphragm is formed by etching a substrate. This substrate has a first surface provided with a depression by isotropic dry etching, and a second surface opposite the first surface. Furthermore, a through-hole is formed from the depression to the second surface by anisotropic dry etching. The depression and the through-hole are formed by using one resist mask. The depression has a hemispherical shape or a semi-elliptical spherical shape.