A spread illuminating apparatus of side light type includes a transparent resin plate, a reflector disposed at one major surface of the transparent resin plate, and a light source disposed in a light source space formed toward one end of the transparent resin plate, wherein the reflector includes a main part having a rectangular shape and fold parts formed at peripheral edges of the main part so as to rise up therefrom, slits are formed through portions of the transparent resin plate located inside and off its peripheral edges, and wherein the fold parts of the reflector are inserted though the slits of the transparent resin plate.