To illuminate a prescribed range by the prescribed number of apertures even when the size of a light emitting part of a light source is small and to improve the uniformity of illuminance distribution on an illuminated object and the directional characteristic of luminance.

An optical element has a plurality of faces 12a, 12b which are parallel with each other and respectively have prescribed transmission factors and reflection factors. When it is defined that the number of effective faces having prescribed reflection factors and transmission factors is k, provided that k is an integer of ≥2, the transmission factors and reflection factors of respective faces 12a, 12b are set so that the intensities of light beams when the total number of times of transmission or reflection received by the faces 12a, 12b having the prescribed reflection factors and transmission factors is up to 2k-1, however the total intensities of light beams passed through different routes in the same value 2k-1, become almost the same.