A polarization conversion element includes: a plurality of light transmitting substrates sequentially bonded at a plurality of inclined planes thereof that form an angle of approximately 45° with respect to a light incident face and a light emitting face being approximately parallel to the light incident face; a retardation plate providing a phase difference to incident polarized light; a polarization separation film separating incident light into two types of polarized light; and an air layer. In the element, the polarization separation film and the air layer are alternately formed along the plurality of inclined planes.