The object of the present invention is to provide an excellent-quality polarization phase difference plate that enables, by a simple structure: decrease in light loss and in oscillation of the intensity of the transmitting emission light through effectively suppressing Fresnel reflection in the polarization phase difference plate; improvements in the optical property, cut in the cost; and decrease in the manufacture inferior. In the polarization phase difference plate, cross-sectional shape of the convex part is formed in a taper shape from the bottom part thereof towards the top part; a flat part is formed at least between the convex parts being adjacent to each other; and the period of the diffraction grating is formed in a size that is equal to or smaller than the wavelength of light to be used.