A cooling device includes: a partition plate for partitioning an interior of a case into a first fluid passage through which first fluid having a high temperature flows and a second fluid passage through which second fluid having a low temperature flows; a heat receiving portion disposed in the first fluid passage; a heat radiating portion disposed in the second fluid passage; and a connection pipe for communicating the heat receiving portion and the heat radiating portion. The heat radiating portion is disposed at an upper side of the heat receiving portion in such a manner that the second fluid from a front side of the heat radiating portion flows into a rear side of the heat radiating portion through a pipe space between the heat radiating portion and the heat receiving portion, and further passes through the heat radiating portion from the rear side toward the front side of the heat radiating portion. Thus, the cooling device has a small size while improving the cooling capacity of the cooling device.