A high performance polarization splitting element and an optical device using the polarization splitting element are provided. According to an embodiment of the present invention, the optical device includes a first periodic structure having a period shorter than a wavelength of used light, a second periodic structure which has a period shorter than the wavelength of the used light and in which a direction of the period is orthogonal to or substantially orthogonal to that of the first periodic structure, and a pair of optical elements disposed so as to sandwich the first periodic structure and the second periodic structure. The second periodic structure is adjacent to the first periodic structure. The first periodic structure and the second periodic structure transmit light having first polarization direction and reflect light having second polarization direction orthogonal to the first direction.