To obtain a Fresnel lens of flat-surface incidence, which is free of the restriction regarding the overall size and which has a short focal point.
Many prism parts 11, 12, of which incidence side is a flat surface 2 and of which outgoing side is a projecting surface, are arranged on the same plane and exhibit one lens function as the Fresnel lens as a whole. The projecting surface of the prism part 11 of a first group close to an optical axis A exhibits lens function by the light reaching a first side 3 to be refracted and emitted on the first side 3, and the projecting surface of the prism part 12 of a second group far from the optical axis A exhibits lens function by having the light that reaches the first side 3 to be refracted and emitted by a second side 4, after total reflection at the first side 3.
YADA YUKIO
ISHIDA SHOHEI
SATO KOICHI
