A polarization element has a polarizer with an aggregate of metal pieces: Plasmon resonance frequency of a metal piece varies according to the polarization direction of a irradiated on it. In the polarization element, the plasmon resonance frequency in a predetermined direction of a metal piece is substantially equal to the frequency of light irradiated on the polarization element. The real part and the imaginary part of permittivity at the plasmon resonance frequency of a metal piece's constituent material and the refractive index (na) of a dielectric layer satisfy a particular relation.