1. A cooling device comprising:a plurality of coolers, each of which is provided in each of a plurality of electronic devices that are arrayed in a layered shape;
a water-supply pipe that has a plurality of branch pipes and supplies a coolant to the plurality of coolers, each of the branch pipes being coupled with each of the plurality of coolers;
a waste pipe that has a plurality of branch pipes, each of which is coupled with each of the plurality of coolers, the coolant having passed through the plurality of coolers being exhausted to the waste pipe;
a circulation pipe that couples an inlet of the water-supply pipe with an outlet of the waste pipe and has a pump configured to discharge the coolant and a coolant cooler configured to cool the coolant; and
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.