A backlight unit is provided. The backlight unit includes: a mold frame having a predetermined receiving space formed therein; a light guide plate disposed in the receiving space of the mold frame, and having an inclined surface formed on one side of the top surface so as to be inclined toward the inner side; a light source disposed between the light guide plate and the mold frame to emit light to the light guide plate; and a flexible printed circuit board, on which the light source is mounted, and which is supported in contact with the top surface of the light guide plate, wherein a stepped portion is formed on one end of the light guide plate, including a flat adhesion surface positioned at a height lower than one end face of the light guide plate.