A backlight unit with a new configuration is disclosed. The backlight unit includes: a main support formed using a mold which opens upward; a light source unit disposed on one side of the main support; a light guide plate disposed parallel to the light source unit and configured to convert dot light emitted from the light source unit into two-dimensional light; and optical sheets disposed on the light guide plate. The main support is provided with a light incident space, which allows light emitted from the light source unit to be entirely and evenly entered to the light guide plate, on its one side opposite to the light source unit.