An IO system board included in an electronic device includes, in addition to a first section board that includes first ventilating holes and second section board that includes second ventilating holes, a third section board that includes third ventilating holes. Accordingly, a larger amount of cooling air is taken in via an air intake surface of a rack of the electronic device, flows into a casing of the IO system board, and then flows over a first sub circuit board, thus cooling a first heat-generating component.