Abstract: A process for separating enriched oxygen and argon from air through pressure swing adorption by using an adsorbent which is capable of selectively adsorbing nitrogen. Product gas is recovered from one adsorption column in which the adsorption step has already been completed by moving the gas to another adsorption column in which regeneration of the adsorbent by pressurization with the product gas has already been completed on the basis of pressure equalization. In this case, at the same time as the gas is being moved from the feed end of one column to the feed end of another, the gas may also be moved from the effluent end of the former to the effluent end of the latter. In this way, it is possible to stably and readily obtain an enriched oxygen gas having a lowered nitrogen content at an increased specific product and a lowered specific power consumption.