A lighting unit comprises a light source, a light guiding plate for guiding light emitted from the light source, a reflecting sheet disposed at least a portion of a surface of the light guiding plate, and a casing configured to store the light guiding plate provided with the reflecting sheet, wherein a space between the casing and the light guiding plate is separated from a space above the light guiding plate by an extended portion formed by extending the reflecting sheet disposed on the surface of the light guiding plate.