A small variable capacitor including a movable section composed of a movable electrode supported by a supporting section. A driving electrode and a detecting electrode are provided facing the movable electrode. When an external bias voltage is applied between the movable electrode and the driving electrode, Coulomb force is generated between them. Due to that, the movable section is attracted toward the driving electrode while keeping a balance between its own resilience force and the Coulomb force. At this time, part of the movable section facing the detecting element is displaced more than the other part of the movable section facing the driving electrode. Thereby, because an electrostatic capacity between the movable section and the detecting electrode is inversely proportional to the average distance, a large electrostatic capacity may be obtained and variability of the electrostatic capacity becomes large.