An optical device which leads light beams emitted by a light source to a predetermined illumination area comprises first and second light leading members. The first light leading member includes a first incident surface configured to be entered the light beams emitted by the light source and a first outgoing radiation surface configured to emit the light beams. The second light leading member includes a second incident surface configured to be entered the light beams emitted from the first outgoing radiation surface of the first light leading member and a second outgoing radiation surface configured to emit the light beams. The first outgoing radiation surface has a shape different from that of the first incident surface. The second outgoing radiation surface has a shape different from that of the second incident surface.