To eliminate luminance unevenness at the central part and the end of a backlight unit of a liquid crystal display device using LED as a light source.

A diffusion sheet is arranged above the LED light source. In the central region of the diffusion sheet, the diffusion angle of outgoing light when a light beam is made incident on the diffusion sheet perpendicularly to the surface thereof, changes periodically along the in-plane predetermined direction of the diffusion sheet. In a diffusion angle distribution map which is drawn by taking the relative positions in the diffusion sheet in the in-plane predetermined direction on the horizontal axis and the diffusion angles at the relative positions in the in-plane diffusion sheet on the vertical axis, there are a plurality of peak values and a plurality of bottom values in the diffusion angles. In the edge region of the diffusion sheet, an area having a larger diffusion angle than the peak value of the diffusion angle in the central region of the diffusion sheet, is provided.