To provide a capacitor which is changed in capacitance by a DC bias applied from outside, capable of decreasing the number of laminated layers of an electrode provided to its capacitor main body, and capable of reducing a voltage necessary for applying a DC bias.

A DC bias applying electrode 25, a capacitance acquiring electrode 26, and a grounding electrode 24, are provided to the capacitor main body 23. The grounding electrode 24 is made to function not only as an electrode for applying a DC bias, but also as an electrode for acquiring capacitance.