An optical element transmits incident light having a particular polarization direction mainly by 0-order transmission and diffracts incident light having a perpendicular polarization direction. The optical element includes a periodic structure having a period equal to or greater than the wavelength of the incident light. The periodic structure includes first and second subwavelength concave-convex structures formed perpendicularly adjacent to each other in each period of the periodic structure. The first and the second subwavelength concave-convex structures have a period less than the wavelength of the incident light. A filling factor and a groove depth of the first and the second subwavelength concave-convex structures are determined such that they have the same effective refraction index with respect to the incident light having the particular polarization direction and a phase difference π with respect to the incident light having the particular polarization direction.