To secure a hygienic surface of a base material by a method in which air polluting substances are decomposed by exciting the photoactivity and hydrophilicity of the coating surface, the surface of the base material is purified to acquire aesthetic effects, and active oxygen is generated by a photoreactive reaction to generate sterilizing/antibacterial effects.

The on-site coating method using the photocatalytic action of titanium oxide, by receiving light energy, oxidation-decomposes harmful substances such as nitrogen oxide and automobile exhaust gas into nitrates to keep the surface of an outer wall material and others beautiful and forms a fine membrane thickness. In this way, the surface of a coating film is made to develop an ultra-hydrophilic function and a photoreactive function, and the decomposition of air polluting substances such as organic chlorine compounds and nitrogen oxide and an antibacterial interface can be generated.