An illumination device for illuminating outdoor areas, comprising: a main body supported by a support member; an upper cover portion 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 power supply unit being disposed between the support member and the LED light emitting part, wherein the upper cover portion includes a plurality of radiation fins provided on a top portion thereof and a plurality of grooves defined between adjacent radiation fins, wherein the main body is arranged to slant downward toward the support member and the radiation fins extend toward the support member, and characterized in that, a height of the radiation fins at a side where the LED light emitting part resides is greater than a height of the radiation fins at a side where the power supply unit exists, wherein a thickness of a section of the illumination device where the LED light emitting part exists is smaller than a thickness of a section of the illumination device where the power supply unit exists, wherein the illumination device further comprises a power supply containing unit protruding downward from the main body to contain the power supply unit therein and provided near the support member, and a light emitting panel provided at a lower side of the main body, and wherein a light control function unit having a function of controlling the light coming from the light emitting panel is provided on an outer surface of the power supply containing unit, the light control function unit including a slant surface (21 a) inclined downward in a direction away from the light emitting panel. a main body supported by a support member; an upper cover portion 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 power supply unit being disposed between the support member and the LED light emitting part, wherein the upper cover portion includes a plurality of radiation fins provided on a top portion thereof and a plurality of grooves defined between adjacent radiation fins, wherein the main body is arranged to slant downward toward the support member and the radiation fins extend toward the support member, and characterized in that, a height of the radiation fins at a side where the LED light emitting part resides is greater than a height of the radiation fins at a side where the power supply unit exists, wherein a thickness of a section of the illumination device where the LED light emitting part exists is smaller than a thickness of a section of the illumination device where the power supply unit exists, wherein the illumination device further comprises a power supply containing unit protruding downward from the main body to contain the power supply unit therein and provided near the support member, and a light emitting panel provided at a lower side of the main body, and wherein a light control function unit having a function of controlling the light coming from the light emitting panel is provided on an outer surface of the power supply containing unit, the light control function unit including a slant surface (21 a) inclined downward in a direction away from the light emitting panel.