PURPOSE: To prevent the leakage of H2 and the isotope thereof, by providing an oxidation treatment apparatus for subjecting H2 and the isotope to oxidation treatment, a blower for feeding air into said apparatus and a backfire preventing device for carrying out safer treatment of a cold trap regeneration system.

CONSTITUTION: H2 and the isotope thereof exhausted by a gas withdrawing spot 12 as a cold trap is regenerated are sent to a backfire preventing device 17 by an exhaust pump 16 and sent to an oxidation treatment apparatus 19 while mixed with air sent from a blower 18 to be subjected to oxidation treatment therein. Water and a gas formed by oxidation are respectively discharged from a pipe 20 and an exhaust cylinder 21. The backfire preventing device 17 has a flame extinguishing element constituted of a metal net. By this flame extinguishing element, the temp. of combustion is cooled and combustion is prevented. Therefore, the leakage of H2 and the isotope thereof to be exhausted from the cold trap are prevented.