PURPOSE: To form the whole heat exchanger prominent in the anticorrosion of a base material by a method wherein a synthetic resin film is formed on the base material of heat exchanging element and moisture absorbing agent of silica gel, active alumina or the like is adhered solidly to the base material of the heat exchanging element.

CONSTITUTION: The rotary type exchanging element, provided with a honeycomb structure formed by the aluminum foil of 20μm thickness after degreasing the surface thereof previously, is dipped into the solution of acrylic resin, thereafter, is picked up and dried for 10min. in a warm-air drying furnace having temperature of 80°C to form the film 6 of acrylic ester resin on the aluminum 3. Subsequently, the heat exchanging element is dipped into the solution of silica gel added with 3% of sodium silicate again, thereafter, is picked up and dried for 30min. under the temperature of 80°C to form the moisture absorbing layer 5. The synthetic resin film is formed at first on the base material of the heat exchanging element, therefore, anticorrosion effect is high and bonding property between the formed synthetic resin film and silica gel is good.