A liquid crystal display device includes a cover bottom, a reflection sheet over the cover bottom, lamps over the reflection sheet, a diffuser plate over the lamps, a plurality of optical sheets over the diffuser plate, a guide panel of a rectangular shape surrounding edges of the diffuser plate and the plurality of optical sheets, the guide panel including fixing ribs at an inner surface thereof, a liquid crystal panel over the plurality of optical sheets and including first and second substrates and a liquid crystal layer therebetween, a top cover covering edge portions of a front surface of the liquid crystal panel and combined with the guide panel and the cover bottom, wherein the fixing ribs contact edges of the diffuser plate such that a force is applied to the diffuser plate.