An optical element that is made of a transparent medium L1 rotationally symmetric relative to the central axis 2 with a refractive index greater than 1, characterized in that the transparent medium L1 has a first transmissive surface 11, a first reflective surface 12, a second reflective surface 13 arranged at the opposite side to the image plane 5 relative to the first reflective surface 12 and a second transmissive surface 14 arranged at the image plane 5 side relative to the second reflective surface 13 and that the flux of light entering the transparent medium L1 goes into it by way of the first transmissive surface 11 so as to be reflected to the opposite side to the image plane 5 by the first reflective surface 12 and then to the image plane 5 side by the second reflective surface 13 to form a substantially Z-shaped optical path before going out from the transparent medium L1 at the image plane 5 side by way of the second transmissive surface 14 in the order of forward ray tracing.
