PURPOSE: To obtain a light converging plate which is improved in transmissivity and can improves an abrupt decrease in luminance by increasing the refractive index of the light converging plate, which has a plane as its one surface and also has plural nearly triangular prismatic bodies arrayed on the other surface, from the plane to other surfaces of the prismatic bodies.

CONSTITUTION: The light converging plate 1 is sectioned almost in a right-angled isosceles triangle shape and provided with four refractive index layers which show variation in the refractive index in the light converging plate 1. Namely, two sides 2 and 3 containing the right angle are larger in refractive index than the side of the plane (incidence surface) 4. Therefore, when a light beam (a) is made incident from the side of the plane (incidence surface) 4 in the normal direction, it is gradually refracted in the light converging plate 1 and reaches a surface 2. Thus, the light beam is gradually refracted in the light converging plate 1 and then the light beam (a) has an angle exceeding the conditions of total reflection to the surface 2 when reaching the surface 2, so light C is projected without totally reflected.