Provided is a cooler including an upper plate configured to have a semiconductor chip to be arranged thereon, a plurality of plate-like fins arranged under the upper plate, and a coupling bar coupled to the plate-like fins. The coupling bar has a main-body portion and a plurality of comb-tooth portions protruding from the main-body portion into the flow channel, the cooler includes a plurality of openings in a plane orthogonal to an extending direction of the plate-like fins, and the openings are defined at least by the comb-tooth portions and the plate-like fins, and the openings include a first opening provided in a first flow channel that does not run below the semiconductor chip, and a second opening provided in a second flow channel that runs below the semiconductor chip, where the second opening is larger than the first opening.