A backlight device for use in a display device includes a light source device and a light diffusion member. The light source device includes a plurality of light sources. The light diffusion member includes a light transmission body and reflectors. The light transmission body includes a light receiving surface facing a first one of the light sources for receiving the light emitted from the first light source and a light output surface facing away from the light receiving surface for outputting the light transmitted through the light transmission body. The reflectors are attached to the light transmission body and include first and second reflection surfaces oriented such that the light received from the first light source through the light receiving surface is reflected by the first and second reflection surfaces while the light passes through the light transmission body toward the light output surface.