An actuator includes: an electrostatic actuation mechanism including a stationary electrode and a movable electrode; a first movable part driven by the electrostatic actuation mechanism; a first elastic support part that elastically supports the first movable part; an electret formed in at least one of the stationary electrode and the movable electrode; and a drive control unit that controls application of voltage to the electrostatic actuation mechanism. In the actuator a plurality of stable states are set in which the first movable part is positioned at a stable position at which an electrostatic force generated by the electret matches with an elastic force exerted by the first elastic support part or at a stable position near such stable position. By applying a voltage to the electrostatic actuation mechanism, the first movable part may be displaced from any stable position to another stable position.