To prevent sticking of dust to a pipe body and easily eliminate stuck dust by providing a layer containing a photocatalyst semiconductor material in a surface contacted with liquid and irradiating the same with ultraviolet rays.

Although different depending on the kind of a base material used for piping or the degree of surface polishing, the contact angle of a surface with water is several to several tens of degrees. A layer containing a photocatalyst material is formed in the surface of the base material by using a coating agent combining a titanium oxide as a photocatalyst material with a silicone resin, the contact angle of the surface with water is reduced nearly to 0 by irradiating the same with sufficient ultraviolet rays and, by greatly increasing the hydrophilic property of the surface, sticking of dust inside the piping is prevented, the number of times of cleaning is reduced, stuck dust is easily eliminated only by water washing and costs are reduced without needing any special cleaners.