An actuator includes a movable plate having a plate shape, a pair of axial parts that is elastically deformable and supporting the movable plate rotatable, and a tension adjuster adjusting tension on an axial direction of the pair of the axial parts and including a torsional axis that is formed jointly or integrally with one of the axial parts and disposed orthogonally to the axial direction of the axial parts, and a drive source that torsionally deforms the torsional axis, wherein the torsional axis is torsionally deformed through the action of the drive source and a spring constant of the pair of the axial parts is adjusted by adjusting the tension on the pair of the axial parts.