The problem addressed by the present invention is, when purifying a target gas from a mixed gas containing a target component using pressure swing adsorption, preventing effects of impurity components that reduce the purification capacity of an adsorbent while recovering high-purity target gas with good efficiency. This method repeatedly carries out, for each adsorption unit, a cycle that includes an adsorption step wherein the mixed gas is introduced into adsorption units, in a state where the adsorption units are at relatively high pressure, by pressure swing adsorption carried out using a plurality of adsorption units filled with the adsorbent, which selectively adsorbs impurity components, the adsorbent is made to adsorb the impurity components in the mixed gas, and a gas in which the target component is enriched is exhausted from the adsorption units and a pressure reduction step wherein pressure is reduced in the adsorption units and gas is exhausted from the adsorption units. Each adsorption unit includes first and second adsorption tanks (10A - 10D, 20A - 20D) connected in series. In the pressure reduction step, switching between a state in which the first and second adsorption tanks are linked and a state where the same are not linked is carried out by an on-off valve (16) provided between the first and second adsorption tanks.