An illumination device includes: a main body supported by a support member; an upper cover portion for covering an upper portion of the main body; and an LED light emitting part and a power supply unit, both of which are fixed to a lower side of the upper cover portion. The upper cover portion has a plurality of radiation fins provided on a top portion thereof and a plurality of grooves defined between the adjacent radiation fins, the grooves being inclined downward toward a peripheral edge of the upper cover portion.