A tandem type backlight comprises plural light-emitting units (11) including at least one point light source (5) and a light guide plate (7) for causing light from the at least one point light source to be diffused and surface-emitted. In each of the light-emitting units (11), a length X of a light guide area (9) is set so that an area, on a boundary surface between a light-emitting area (10) and the light guide area (9), of a cross-section of a light beam that is emitted from the at least one point light source (5) and is diffused in the light guide plate (7) is equal to or larger than an area of the boundary surface (interface). Moreover, a length X, in a length direction D1, of the light guide area is smaller than a length Y, in the length direction D1, of the light-emitting area.