A backlight device comprising: a reflection sheet having a reflection surface which is divided into reflection regions by a plurality of partitions that are each a ridge-shaped projection; light sources disposed in the respective reflection regions of the reflection surface; a luminance uniformizing plate, the material itself of the luminance uniformizing plate having translucency but being not transparent, that transmits light emitted by the light sources and light reflected off from the reflection sheet, by receiving the light with a first surface of the luminance uniformizing plate and emitting the received light from a second surface of the luminance uniformizing plate, the first surface being facing the reflection surface of the reflection sheet, the second surface being located on a side of the luminance uniformizing plate opposite to the first surface; and a diffusion plate that receives, diffuses and emits the light emitted from the second surface, wherein the luminance uniformizing plate includes a light-transmittance region opposed to each of the light sources, a light-transmittance region opposed to each of the vertex portions of a corresponding one of the plurality of partitions, and a high light-transmittance region arranged between the light-transmittance region opposed to each of the light sources and the light-transmittance region opposed to each of the vertex portions of a corresponding one of the plurality of partitions, the high light-transmittance region being higher in light-transmittance per unit area than the light-transmittance region opposed to each of the light sources and the light-transmittance region opposed to each of the vertex portions. a reflection sheet having a reflection surface which is divided into reflection regions by a plurality of partitions that are each a ridge-shaped projection; light sources disposed in the respective reflection regions of the reflection surface; a luminance uniformizing plate, the material itself of the luminance uniformizing plate having translucency but being not transparent, that transmits light emitted by the light sources and light reflected off from the reflection sheet, by receiving the light with a first surface of the luminance uniformizing plate and emitting the received light from a second surface of the luminance uniformizing plate, the first surface being facing the reflection surface of the reflection sheet, the second surface being located on a side of the luminance uniformizing plate opposite to the first surface; and a diffusion plate that receives, diffuses and emits the light emitted from the second surface, wherein the luminance uniformizing plate includes a light-transmittance region opposed to each of the light sources, a light-transmittance region opposed to each of the vertex portions of a corresponding one of the plurality of partitions, and a high light-transmittance region arranged between the light-transmittance region opposed to each of the light sources and the light-transmittance region opposed to each of the vertex portions of a corresponding one of the plurality of partitions, the high light-transmittance region being higher in light-transmittance per unit area than the light-transmittance region opposed to each of the light sources and the light-transmittance region opposed to each of the vertex portions.