A light guide plate has a light guide plate body and at one side thereof a curvedly descending portion formed by curving front and rear surfaces of the light guide plate, with the surface to surface distance kept uniform, to a coaxial arcuate configuration so as to extend towards a direction of a rear surface of the light guide plate body. Spot light sources disposed in face to face relation with a free end face of the curvedly descending portion are arranged to be displaced towards the front surface of the light guide plate from a mid-center plane between the front and rear surfaces of the curvedly descending portion.