Film forming method of corrosion resistant film, corrosion resistant member on which corrosion resistant film is formed, heat exchanger, and fuel cell system

A film forming method of a corrosion resistant film, comprising:

• storing an aqueous solution containing sulfate ions and fluoride ions in a storage portion, the storage portion being part of a heat exchanger with a wall portion of the storage portion formed of a substrate made of aluminum, the substrate being in contact with the aqueous solution during the storing;
• and
• heating the substrate by a heat of a thermal fluid that is introduced to the heat exchanger, the thermal fluid having a temperature higher than a boiling point of the aqueous solution so that heat is transmitted to the aqueous solution via the wall portion to boil the aqueous solution on a surface of the substrate to form a corrosion resistant film on the surface of the substrate, the corrosion resistant film containing oxygen, fluorine, and sulfur derived from the aqueous solution and aluminum derived from the substrate.