A cooling device includes a base plate to a rear surface side of which an under-floor device is attached; a heat radiating unit attached to a front surface side of the base plate and radiating heat conducted from the under-floor device via the base plate; a cover surrounding the heat radiating unit and including a side opening capable of causing traveling wind to flow therein and causing a traveling wind flown therein to flow out, in opposite side surfaces facing a traveling direction of a vehicle; and an guide plate guiding traveling wind flowing in from the side opening to the heat radiating unit by blocking at least part of a gap area between a surface connecting the opposite side surfaces of the cover and the heat radiating unit, the guide plate being provided in a side gap area between a side surface of the cover and the heat radiating unit on a side from which the traveling wind flows in.