In a lighting unit (UT1) of the present invention comprising a light guiding plate (3), casings (5, 6) covering at least a pair of side portions and a lower surface 3f of the light guiding plate so as to form a column-shaped light source unit storage space (103) along a side surface (3a) of one of the side portions, a reflecting sheet (4) disposed between the lower surface of the light guiding plate and a bottom surface of the casing such that an end (4a) thereof protrudes into the light source unit storage space, and a light source unit (L) inserted into the light source unit storage space and having a light source (1), a reflector (2), and a light source holding component (7), wherein the light source is bar-shaped and disposed along the side surface (3a) of the light guiding plate, the reflector is plate-shaped and encloses the side surface (3a) of the light guiding plate such that the light source is located inside thereof and one end thereof is located under the end (4a) of the reflecting sheet, and the light source holding component is disposed on the reflector for holding both the end portions of the light source, a structure (A) for inhibiting the end (2a) of the reflector from entering between the light guiding plate and the reflecting sheet when the light source unit is inserted into the light source unit storage space or for confirming whether or not the end of the reflector has entered is provided.