In one embodiment, an illumination device includes a light guide, a light source and prisms. The light guide has a side surface and first and second main surfaces. The light source emits light to the side surface in a first emission direction. The prisms are provided on the second main surface. The second main surface has first and second areas. The prisms include first prisms in the first area and second prisms in the second area. A first virtual line connecting apexes of the first prisms is inclined with respect to the first main surface. A distance between the second area and the first main surface is greater than a distance between the first area and the first main surface.