A photocatalyst element structure includes a photocatalyst element that includes a flat photocatalyst sheet and an undulating photocatalyst sheet overlapped on the flat photocatalyst sheet. The flat photocatalyst sheet and the undulating photocatalyst sheet include a porous titanium foil having a non-periodic spongy structure impregnated with anatase titanium dioxide particles. The photocatalyst element structure can include a plurality of the photocatalyst elements so that the flat photocatalyst sheet and the undulating photocatalyst sheet alternate.