Using a distance L between the centers of light sources 12, 12; a refractive index n of an optical element 15; a thickness d of the optical element; a distance W from the center of the light source to the optical element; a refractive index n0 of air; an angle of incidence θ1 of light emitted from the light sources and coming into the optical element, relative to the direction of optical axes; an angle of refraction θ2 of light, incident on the optical element, in the optical element; a diameter of each light source as D; and a maximum tangential angle a formed between a tangential line in contact with an outer surface of a luminance distribution generating layer 18 and a plane orthogonal to the optical axes, there is included a maximum tangential angle a satisfying x>L/2−D/2 when calculating a travel range x of a split image of the light sources in a direction normal to the optical axes using (1) n0 sin(a)=n sin(a−θ2), (2) n0 sin θ1=n sin θ2 and (3) x=W tan θ1+d tan θ2. This facilitates uniformalizing of front luminance distribution.