To provide a two bed type pressure change adsorption method for recovering a main gas component in the purity more than 99% from the supplied gas containing the main gas component and one or more kind impurities.

(a) A stage in which one or more kind impurities are removed by passing the supplied gas through a first adsorption bed, (b) a stage in which a pressure change adsorption cycle is executed at the first bed, (c) a stage in which the effluent gas from the first bed is separately sent to at least two different tanks to prepare for later purging and pressuring of the bed, (d) a stage in which the gas mixture containing the main component in higher concentration than that of the second tank is stored at the first tank, (e) a stage in which the mixture of the main component from the second tank is returned to the first adsorption bed during regeneration stage, (f) a stage in which the mixture of the main component from the first tank is returned to the first adsorption bed during regeneration stage, (g) a stage in which the stages (a)-(f) are executed simultaneously and in non-parallel flow in the second bed and (h) a stage in which the gas flow of product is recovered are provided.