To provide photocatalytic units corresponding to the characteristics of zinc oxide fine crystal bodies.

(a) A zinc oxide fine crystal body 220 is packed into a cylinder of a coaxial cylindrical unit 200. The zinc oxide fine crystal body 220 can act also as a photocatalyst even in visible light. An ultraviolet light source or a fluorescent lamp 210 is installed at the inside of the coaxial cylindrical unit 200, natural light or a fluorescent lamp is emitted from the outside, thus the photocatalyst can be efficiently activated. (b) A flat square unit 200' utilizing plane like glass is also passible. From the two transparent faces provided at the surface and back of the plane like unit 200', natural light or a fluorescent lamp can be emitted. By using the unit 200, a space where a light source lies and a space in contact with gas exhibiting photocatalytic effect are separated, and the corrosion of the surface in the light source by photocatalytic reaction and the sticking of reacted products to the surface of the light source can be prevented.

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