A sound hole is provided in a silicon substrate. A diaphragm electrode is secured to the upper surface of the silicon substrate via at least one fixed end so as to cover the sound hole of the silicon substrate. The diaphragm electrode is provided with four projections extending in respective directions of diameter orthogonal to each other. The fixed end is provided in one of the four projections. Hinge shafts are provided in the other three projections. A backplate electrode is provided above the diaphragm electrode so as to form a capacitor.