A double-sided emitting backlight unit has a first light-emitting surface for illuminating a first liquid crystal display panel disposed to face the first light-emitting surface, a second light-emitting surface provided parallel to the first light-emitting surface to illuminate a second liquid crystal display panel that is smaller than the first liquid crystal display panel and disposed to face the second light-emitting surface, and a peripheral surface extending between the first and second light-emitting surfaces and each groove having a light-receiving surface that receives light from a light source. The second light-emitting surface is a prism surface provided with a multiplicity of grooves extending parallel to the light-receiving surface and having a triangular section. The grooves in a part of the second light-emitting surface that corresponds to the second liquid crystal display panel in a direction perpendicular to the light-receiving surface are larger than the grooves in the rest of the second light-emitting surface in terms of at least one factor selected from among the following: the depth of the grooves; the angle between the second light-emitting surface and an inclined surface of each groove extending from the second light-emitting surface to the apex of the triangular section in a direction away from the light-receiving surface; and the number of grooves per unit length in the direction perpendicular to the light-receiving surface. With this configuration, the quantity of light per unit area emitted from a part of the first light-emitting surface corresponding to the second liquid crystal display panel is larger than that emitted from the rest of the first light-emitting surface.