To provide a cooling device that is arranged on the exhaust side of the outdoor unit heat exchanger of an air conditioner for indoor cooling to cool down the exhaust hot air from a radiator.

A cooling device comprises a water-absorber unit with many water-absorbing sheets erected at intervals and a water vessel receiving the unit to wet the lower parts of the water-absorbing sheets with water, and it is arranged on the exhaust side of the outdoor unit heat exchanger of a cooler. The exhaust hot air of a cooler outdoor unit is allowed to pass through the intervals of the water-absorbing sheets of the water-absorber unit, and the exhaust hot air is cooled and diffused. Particularly, the separate body is provided with a case storing the water vessel and the water-absorber unit that is arranged in the vessel in such a manner that it can be submerged, and the case is attached to the outdoor unit. It is desirable that the water-absorber unit can be changed.