PURPOSE: To treat a large gas volume, lower the effect of deflecting flow, and efficiently reproduce an adsorbent by collectively setting elements of an environment tritium cleaning system in the inside of a duct casing.

CONSTITUTION: The fine powder, etc., are removed from an ambient gas 21 flowing in by a prefilter 24 and a highly functional particle filter 25 while the gas passing a dehumidifier 22 and a heating coil 23. Then, the gas flows in an adsorbent packed layer 30 through a heating coil 26 and a catalyst packed layer 27, tritium steam is adsorbed, and the resulting gas is led to a ventilation fan through a highly functional particle filter 33. The adsorption capacity of the adsorbent is limited and the adsorbent needs to be reproduced. For this, coiling-type separating valves 28, 32 are installed in both sides of the layer 30 and while a heating coil 31 is separated from a cooling coil 29 at the time of reproduction, the gas to be reproduced is led to flow in and heated by the coil 31 to evaporate the moisture of the layer 30. The moisture is condensed by the coil 29 and removed, so that the adsorbent is reproduced. Also, a good effect that deflecting flow is prevented is achieved by utilizing the valves 28, 32 and the possibility of troubles is lowered.