formed on the inside wall of the regenerator 1a by the foregoing film forming operation of the high temperature regenerator 1a above a composite oxide film having a good corrosion resistance can be formed on the inside wall of the high temperature regenerator to be exposed to the most severe corrosion conditions in the vapor absorption refrigerator and the corrosion problems due to the refrigerating operation of the vapor absorption refrigerator can be overcome furthermore the composite oxide film can be also formed on the inside wall of the high temperature refrigerator in the following manner constituent members of a high temperature refrigerator are defatted and cleaned as they are and then washed with an acid to remove scales from the surfaces of the constituent members then the constituent members are immersed in a film forming solution containing molybdate ions with a ph of 9 to 11 with heating the film forming operation by immersion is preferably carried out in an immersion tank under a pressure of 50 to 60 kg cm 2 at a temperature of 130 u00b0 c or higher below 130 u00b0 c fe 3 o 4 is hardly formed on the surfaces of the constituent members of ion based material it is necessary to make the ph of the film forming solution alkaline and control the potential on the surfaces of the.