A backlight device is provided. A backlight device according to an exemplary embodiment of the present invention includes: a lower cover enclosing a light guide plate and having a bottom cover and a side cover; and a printed circuit board attached to the lower cover and mounted with the light source, wherein the first opening is formed in the lower cover. The light source is inserted into the first opening and is positioned on an inner surface of the lower cover, and the printed circuit board is positioned at the outer surface of the lower cover.