PURPOSE: To generate a water film on the entire surface of plate fins and to improve the cooling efficiency by providing a porous member for passing water in contact with the upper end of the fins of a heat exchanger, providing a sprinkling tank above it, and sprinkling the water in the tank at the fins through the member.

CONSTITUTION: A porous member 40 for passing water is provided in contact with plate fins 31 of a heat exchanger 30 between a sprinkling tank 15 and the upper end of a heat exchanger 30. The tank 15 is provided at its bottom of a high position with a sprinkling port 36. The water overflowed from the port 36 is continuously fed to the upper surface of the member 40 and dropped to the fins 31 of the exchanger 30 through the member 40. The member 40 is formed of laminated glass wool 41 and sandwiched between the upper ends of the fins 31 and the lower surface of the tank 15. The water droplets adhered to the fins 31 via the wool 41 are evaporated by the air supplied by a fan 14, and exhausted from an exhaust port 12. Thus, the fins 31 are thoroughly sprinkled to improve the cooling efficiency.