PURPOSE: To reduce the number of process steps for thereby simplifying an entire manufacturing operation, by applying a chemical film treatment on the flat and smooth surface of base material and by oxidizing the film in a vacuum glass at a predetermined temperature for exhausting vacuum pressure, when a selective absorption film is being formed on the heat collecting board of vacuum glass tube-shaped collector.

CONSTITUTION: A chemical film treatment is undertaken by integrally connecting an iron-based heat collecting board molded and finished in a predetermined shape with a heat medium tube and applying a coating treatment fluid over the surface. After being dried, the heat collecting board and the heat medium tube are secured in place inside a glass tube. Then, the assembly is heated up to about 400W600°C in a heating furnace and oxidized (a) in an atmosphere at an elevated temperature for about one hour. Subsequently, a vacuum inside a glass tube is continuously exhausted (b) for about two hours, while maintaining the vacuum at a constant temperature and allowing the gas to emit from the surface of heat collecting board. Finally, the assembly is allowed to cool naturally (c), and an exhaust port is sealed at the temperature of about 250°C.