To provide a preprocessing method for an air liquefaction separation apparatus capable of adsorbing and removing N2O by a simple constitution and being easily applied to an existing preprocessing apparatus, and a preprocessing apparatus.

One second adsorption unit 12 for adsorbing and removing N2O in material air is installed in the downstream side of a pair of first adsorption units 11A, 11B for adsorbing and removing carbon dioxide and moisture in the material air. The regeneration process of the second adsorption unit 12 and the adsorption process are executed during the adsorption process of the first adsorption units 11A, 11B.

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