A variable capacitor includes a metal oxide film having a perovskite structure, first and second electrode films having the metal oxide film placed therebetween and to be coupled to an external voltage source, and a bias voltage source configured to provide a bias voltage that is applied in series or parallel to a capacitance of a capacitor including the metal oxide film and the first and second electrode films, wherein the bias voltage applied by the bias voltage source to the capacitance is adapted to maximize a voltage dependency of a relative permittivity of the metal oxide film.