According to one embodiment, an illumination device includes a light guide, a light source device and an optical sheet. The light guide has an emission surface and side surfaces which intersect the emission surface, and at least one side surface is located inside a display area. The light source device emits light to the light guide. The optical sheet is provided on the emission surface and is opposed to the display area. The optical sheet has an edge portion which covers an area between the one side surface and an edge of the display area, and a transmittance adjustment area which is provided in the edge portion and reduces a transmittance of the edge portion.