A spread illuminating apparatus of side light type includes a transparent resin plate integrally composed of a light conductor plate portion and a housing frame portion, a light reflecting sheet, and a light source, wherein an opening for housing the light source is provided at a side portion of the transparent resin plate, slits are provided along a boundary between the light conductor plate portion and the housing frame portion, and wherein a gate for injecting resin into a molding die cavity for the transparent resin plate is positioned outside the boundary of the light conductor plate portion and the housing frame portion and is positioned also between the opening and one of slits which are provided toward the side portion of the transparent resin plate having the opening and which are located clear of the opening.