To provide a polarization separating element which can be used from an ultraviolet region up to a near-infrared region, has a wide opening and has a high extinction ratio.

The polarization separating element 1 is provided with a first prism 10, a second prism 20 and a flat plate 30 interposed between them. The first prism 10 is provided with a first incident surface 11 and a first transmission light emission surface 12 intersecting the first incident surface 11 at a prescribed angle. The second prism 20 is provided with a second transmission light emission surface 21 through which the transition light from the first prism 10 is emitted to the outer part and a second transmission light emission surface 22 intersecting the second transmission emission surface 21 at a prescribed angle. The flat plate 30 is held between the first transmission light emission surface 12 and the second transmission light incident surface 22. The first prism 10 and the second prism 20 are formed of Li2B4O7 and the flat plate 30 is formed of α-SiO2, and a first reflected light emission surface 13 for transmitting reflected light reflected by the first transmission light emission surface 12 to the outer part is formed on the first prism 10.