PURPOSE: To obtain a heat exchanger whose liquid in a liquid passage material is cooled effectively by vaporization latent heat of an exudate, by constituting a liquid passage material, which is a heat exchanger material, provided within an air passage with an article made of a porous material permeable toliquid, out of which the liquid in the liquid passage material can ooze.

CONSTITUTION: A heat exchanger pipe 3 as a liquid passage material is arranged within an air passage in a casing 1 which has been so constituted that air passes through the inside through a fan 2 and the heat exchanger pipe 3 is made into an article made of a porous material permeable to liquid. Water 7 supplied into the heat exchanger pipe 3 is permeated through a pipe wall of the same and a wet water film 4 is formed on the external surface of the same. On the one hand, as the air has been passed through the inside of the casing 1, exudated water 4 on the external surface of the heat exchanger pipe 3 is made to evaporate through the flowing air, the heat exchanger pipe 3 is cooled through the evaporation heat and the water 7 in the heat exchanger pipe 3 is cooled also by this cold heat.