An optical element according to the invention constituted by a multilayer structure having a periodic structural portion as at least one region constituted by repetition of a predetermined period, wherein an end surface of the multilayer structure not parallel to layer surfaces of the multilayer structure is used as a light input surface whereas one or each of opposite surfaces of the multilayer structure parallel to the layer surfaces is used as a light output surface. There is an intermediate layer between a medium and a surface of the multilayer structure, the intermediate layer having a refractive index less than the refractive index of the medium. The periodic structural portion of the multilayer structure can be regarded as a one-dimensional photonic crystal. Refracted light from the one-dimensional photonic crystal has good directivity and the direction of the refracted light has strong dependence on wavelength. When this wavelength dependence property is used, a spectroscopic device or a polarized light separating device of high resolution can be achieved without increase in device size.