The first movable electrode is flat, but the second movable electrode is deformed into a convex shape. A dielectric layer is placed on the facing surface of the second movable electrode. By adjusting a voltage to be applied between the first movable electrode and the second movable electrode, an arbitrary distance is secured between the two electrodes by the electrostatic attractive force generated between the two electrodes, and a desired electrostatic capacitance is obtained. When the distance between the two electrodes is shortened, first, at the center, a part of the first movable electrode and a part of the second movable electrode come into contact with each other with the dielectric layer between them. Then, the first movable electrode and the dielectric layer (second movable electrode) come into contact with each other successively from the contact part towards the periphery side, and the contact area gradually increases.