An even titanium oxide film is economically formed on the surface of a substrate. To actualize the film formation, an aqueous titanium tetrachloride solution containing 0.1 to 17% by weight of Ti is applied in a film-like state on the surface of a heat resistant substrate. While the liquid film state is kept as it is, the aqueous titanium tetrachloride solution is heated to 300° C. or more and H2O and HCl in the liquid film are accordingly evaporated to form a titanium oxide film. In the case where the substrate is of aluminum inferior in acid resistance, an acid-resistant film such as an oxide film is previously formed on the surface of the metal substrate.