An illumination device includes a light guide plate having an incident end face and a reflecting surface, and a plurality of light sources provided at the incident end face of the light guide plate. The reflecting surface of the light guide plate has a diffusing pattern for diffusing incident light, the diffusing pattern has a plurality of ridgelines arranged perpendicularly to a propagating direction of the incident light to diffuse the incident light, and the ridgelines are discontinuous in the propagating direction.