An optical element is made of a transparent medium that is rotationally symmetric relative to the central axis with a refractive index greater than 1. The transparent medium has a first transmissive surface at the outermost periphery relative to the central axis, a first reflective surface at the side of the central axis relative to the first transmissive surface, a second reflective surface at the side opposite to the image plane relative to the first reflective surface and a second transmissive surface at the side of the image plane relative to the second reflective surface. The flux of light enters and proceeds through the transparent medium via the first transmissive surface, the first reflective surface, the second reflective surface and the second transmissive surface to form an optical path. The optical path is formed only at a side relative to the central axis.