To provide a photocatalyst structure concerning a photocatalyst functional film, which has a high catalytic reaction efficiency functioning even under a faint light environment with a poor light condition where an ultraviolet amount is small, and additionally has further excellent transparency, flexibility and the like while having an antibacterial function even under a dark place where the photocatalyst does not function.

A surface of a hydrophobic film substrate is hydrophilicidized by a basic layer, and an intermediate layer comprising water-soluble and photocatalytically inactive titanium oxide, and holding a hydrophilic property is formed on the hydrophilic basic layer by a covalent bonding to constitute a structure wherein a photocatalyst layer consisting of water-soluble and photocatalytically active titanium oxide and copper ion is formed on the intermediate layer by the covalent bonding. Therefore, the photocatalyst layer can be formed easily on the hydrophobic film substrate as a uniform and certain coating film to obtain the photocatalyst film having a high photocatalyst activity and constant antibacterial activity together.