A depolarization element in which a plurality of sub-wavelength structure regions having form birefringence are disposed on the surface-layer part of a substrate, wherein a depolarization element is provided having a structure allowing creation of various polarization states. In the depolarization element, the plurality of sub-wavelength structure regions having form birefringence are disposed on the surface-layer part of the substrate. The sub-wavelength structure regions have a sub-wavelength structure comprising ridges and grooves repeatedly disposed at a cycle shorter than the wavelength of the light used. Included as the sub-wavelength structure regions are sub-wavelength structure regions in which the region size in the direction of repetition of projections and indentations in the ridges and grooves of the sub-wavelength structure is within a range that corresponds to 5-25 times the repetition cycle of the ridges and grooves.
