A cooling device includes a plurality of side wall fins formed on an outer surface of a first side wall of a housing, and a plurality of bottom fins formed on a bottom surface of a bottom portion of the housing. A cover member covers the side wall fins and bottom fins from an outer side to form side wall and bottom cooling channels. A chamber is provided that forms a fluid introduction chamber in a direction facing a second side wall so as to communicate with the side wall cooling channel and the bottom cooling channel. A coolant supply device is externally attached to the chamber so as to supply a coolant to the fluid introduction chamber. The side wall fins and the bottom fins are formed in predetermined shapes to adjust an amount of the coolant in the side wall cooling channel and the bottom cooling channel.