A cooling device includes a base plate to a rear surface side of which an under-floor device is attached. A heat radiating unit is attached to a front surface side of the base plate and radiating heat is conducted from the under-floor device via the base plate. A cover surrounding the heat radiating unit and including a side opening is capable of causing traveling wind to flow therein and thereout, in opposite side surfaces facing a traveling direction of a vehicle. A guide plate guides 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 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 traveling-wind flow-in side.