To efficiently perform a photocatalytic reaction and at the same time, easily replace or increase/decrease a photocatalyst material by disposing an ultraviolet lamp at the interior of a cartridge whose inner wall face is specularly fabricated and at the same time, and retaining the photocatalyst material with a photocatalytic coating film formed on the surface of a base material having numerous fine open holes, in a freely attachable/detachable manner.

Two ultraviolet lamps 3 are arranged on the side face of an outer case 2 in the longitudinal direction of a cartridge 1 and a plurality of photocatalyst material are arranged at an equal interval in an arranged inner case 5. In addition, specularly fabricated pyramid-shaped protrusions and recesses are arranged over the entire inner wall face of a wall material 6 forming the outer case 2 and irregularly reflect light emitted from the ultraviolet lamps 3. Further, at the interior of the cartridge 1, the photocatalyst materials having a photocatalytic coating film formed on the surface of a base material having fine open holes, are retained in a freely attachable/detachable manner. In this case, the fine open hole uses a screen having 0.01-3.0 mm weave aperture (a distance between adjacent wires forming a screen) and the numerical aperture of a metal gauze is set to be 3-50%.