A titanium dioxide film (2) having at least photocatalytic activity, whose light linear transmittance corresponding to light having a wavelength of 550 nm is not less than 50% and whose thickness is 0.1 to 5 m or so, is formed on a transparent substrate (1) constituted by a glass plate or the like. Preferably, a precoat film (3), which has optical transmissivity and is constituted by a SiO₂ film having a thickness of 0.02 to 0.2 m or so, is provided between the transparent substrate (1) and the titanium dioxide film (2). Thereby, excellent photocatalytic action and optical transmissivity can be obtained. Moreover, members composing various structures such as a glass window, which are especially required to have optical transparency, can be further provided with photocatalytic activities.