An illumination device includes a light emitting unit, a light guide member, and a support member. The light guide member has a flat plate part that extends in the longitudinal direction and a light guide body, and is molded such that a sectional shape vertical to the longitudinal direction is a hat shape. The support member has a pair of end support parts that support both end parts in the longitudinal direction of the light guide member and a flat plate part-support part that supports a surface of the flat plate part of the light guide member, which is opposite to a side of the light guide body. A support surface of the flat plate part-support part abuts the surface in an entire area in the longitudinal direction of the surface of the light guide member.