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. <EOS>