An upper lid forming an upper portion of a casing is formed by a metal (an aluminum alloy or the like) having a high heat radiation performance. The upper lid serves as a heat sink (a heat radiation member) radiating heat generated from electronic components within the casing to an external portion. A plurality of flat plate-shaped heat radiation fins are provided in an upper surface of the heat sink. A groove forming each of the heat radiation fins is open in a side surface of the heat sink without forming a step.