Compositive wave plate

The invention is intended to solve the problem of a phase shift by the incidence angle dependence of a composite wave plate which is caused when divergent light is incident directly thereon because of occurrence of a phase shift in addition to a desired phase difference of the composite wave plate. The composite wave plate is composed of two laminated wave plates, and respective parameters are set such that: letting θ 1 represent the azimuth angle of the optical axis of the first wave plate with respect to the plane of polarization of incident light thereon in the Poincare sphere representation, θ 2 represent the azimuth angle of the optical axis of the second wave plate with respect to the plane of polarization of incident light thereon in the Poincare sphere representation, Γ 1 represent a phase rotation about the axis of rotation R 1 of the first wave plate in the Poincare sphere representation, and Γ 2 represent a phase rotation about the axis of rotation R 2 of the second wave plate in the Poincare sphere representation, θ 2−θ1 ≠π/2; and that a phase difference ΓT of the composite wave plate satisfies Γ T =(2×θ 1 −π/2)cos Γ 1 +(2×θ 2 −π)cos Γ 2.