In a heat exchanger having tubes and fins, a polyaniline film made of polyaniline and/or a derivative thereof is formed on the surfaces of the tubes and the fins. This polyaniline film is imparted with at least one hydrophilic functional group selected from the class consisting of a primary amino group, a secondary amino group, a tertiary amino group, an ammonium group, a nitric acid group, a carboxyl group, a sulfonic acid group, a phosphonic acid group and a hydroxyl group. Accordingly, the surfaces of the tubes and the fins has good water wettability while maintaining deodorizing and sterilizing functions.