Abstract: An optical element (20) is formed by bonding the faces of first to fourth triangular prisms (21, 22, 23, 24) that form the apex angle, wherein bonding faces (21a, 22b) of the first and second triangular prisms, bonding faces (22a, 23b) of the second and third triangular prisms, bonding faces (23a, 24b) of the third and fourth triangular prisms, and bonding faces (24a, 21b) of the fourth and first triangular prisms are respectively bonded through an optical thin film. Each optical thin film allows the incident light to pass through, or reflects the incident light, depending on the polarization state. The optical element (20) splits an optical path at a first position of the optical thin film, and combines optical paths at a second position of the optical thin film.