When the efficiency of heating with steam is enhanced by adding a condensed water film formation-suppressing amine in a heating step of heating a material to be heated with the steam via a metallic material, the amount of the condensed water film formation-suppressing amine to be added is controlled based on any of the concentration of the condensed water film formation-suppressing amine in a drain, the pH of the drain, the electroconductivity of the drain, the amount of the drain, the amount of the steam, the temperature of the drain, the temperature of the metallic material, and the amount of the metallic material eluted in the drain.