A cooling device includes: coolers; a water-supply pipe that has branch pipes and supplies a coolant to the coolers, each of the branch pipes being coupled with each of the coolers; and a waste pipe that has branch pipes, each of which is coupled with each of the coolers. The coolant having passed through the coolers is exhausted to the waste pipe. The cooling device also includes a circulation pipe that couples an inlet of the water-supply pipe with an outlet of the waste pipe and has a pump to discharge the coolant and a coolant cooler to cool the coolant. The cooling device also includes a bypass flow path that is coupled with at least a top edge portion of the water-supply pipe, bypasses the plurality of coolers, and is coupled with the waste pipe.