In a joint portion of a corner portion at which a raised portion of a side wall portion of a reflection sheet which is mounted on a back surface plate and a side wall portion of a side mold frame intersect each other, an end portion of the side mold frame is formed in a state that the end portion of the side mold frame overlaps the side wall portion of the reflection sheet. Due to such a constitution, a gap which is formed by a displacement of the reflection sheet is closed and hence, it is possible to suppress the intrusion of dusts into the inside of a liquid crystal display device.