To obtain a block material excellent in weather resistance and fouling resistance and having a hydrophilic surface provided with self-cleaning function to environmental pollutants by exciting a natural stone or an imitation structure having a photocatalyst-containing surface layer by irradiation with electromagnetic waves so that action to clean up environmental pollutants in the air and water is exhibited.

A photocatalyst has photocatalytic activity by which organic substances are oxidation-decomposed when it is activated by irradiation with electromagnetic waves of ≤400 nm wavelength and anatase type titanium dioxide is more preferably used as the photocatalyst. A water-soluble or water-dispersible polyester resin is suitable for use as a resin in the case where a surface layer is formed by a coating method. The thickness of the surface layer is preferably 0.01-20 μm. The surface layer exhibits hydrophilic property by the excitation of the photocatalyst with electromagnetic waves and environmental pollutants sticking to the surface are washed off by running water such as rainwater or river water. When the block material is laid on the bottom of a river, a waterway or the like, the shore of the sea, a lake or a slope of a road or the like, a view close to a natural view or an artificial view is obtained.