The atmosphere detritiation system (ADS) for ITER, which is a system provided to remove tritium in building and confinement atmospheres to secure the tritium safety for workers and public in both normal and off-normal conditions based on the ALARA principle, has been designed. In normal condition including maintenance activities, the ADS removes tritium in effluent gas and secondary confinement atmosphere. In the event of off-normal tritium release, the ADS, as a whole, maintains the tritium safety by mitigating the effect of the tritium release according to the operation scenario established based on the present design.