A method for separating a blast furnace gas, comprising the steps of: producing oxygen-enriched air having an oxygen concentration of at least 25 vol%; blowing the oxygen-enriched air into a blast furnace through tuyeres provided in a lower part of the blast furnace; and generating a reformed blast furnace gas by separating and removing carbon dioxide and nitrogen in a blast furnace gas discharged from a blast furnace top, characterized in that: the step of producing the oxygen-enriched air comprises: preparing a first cylindrical container that is rotatable about a center axis and is disposed inside a tubular body, the first cylindrical container is sandwiched by a second cylindrical container and a third cylindrical container, the second and third cylindrical containers (3, 4) are rotatable about the center axis, wherein the first cylindrical container contains a nitrogen-absorbing adsorbent having a nitrogen adsorption that increases with an increase in pressure or a decrease in temperature, the second cylindrical container contains a moisture-absorbing adsorbent and the third cylindrical container contains a moisture-absorbing adsorbent, wherein the moisture-absorbing adsorbents (6, 7) are disposed at the two sides of the nitrogen-absorbing adsorbent; supplying dry airs having different pressures and temperatures to the nitrogen-absorbing adsorbent, the dry airs being supplied to the nitrogen-absorbing adsorbent in directions opposite to each other, wherein the dry airs are airs from which moisture has already been removed by the moisture-absorbing adsorbents (6, 7); conducting a denitrification treatment on an air having a relatively high pressure or a relatively low temperature; and conducting nitrogen enrichment on an air having a relatively low pressure or a relatively high temperature, thereby conducting oxygen enrichment on the air having the relatively high pressure or the relatively low temperature. producing oxygen-enriched air having an oxygen concentration of at least 25 vol%; blowing the oxygen-enriched air into a blast furnace through tuyeres provided in a lower part of the blast furnace; and generating a reformed blast furnace gas by separating and removing carbon dioxide and nitrogen in a blast furnace gas discharged from a blast furnace top, characterized in that: the step of producing the oxygen-enriched air comprises: preparing a first cylindrical container that is rotatable about a center axis and is disposed inside a tubular body, the first cylindrical container is sandwiched by a second cylindrical container and a third cylindrical container, the second and third cylindrical containers (3, 4) are rotatable about the center axis, wherein the first cylindrical container contains a nitrogen-absorbing adsorbent having a nitrogen adsorption that increases with an increase in pressure or a decrease in temperature, the second cylindrical container contains a moisture-absorbing adsorbent and the third cylindrical container contains a moisture-absorbing adsorbent, wherein the moisture-absorbing adsorbents (6, 7) are disposed at the two sides of the nitrogen-absorbing adsorbent; supplying dry airs having different pressures and temperatures to the nitrogen-absorbing adsorbent, the dry airs being supplied to the nitrogen-absorbing adsorbent in directions opposite to each other, wherein the dry airs are airs from which moisture has already been removed by the moisture-absorbing adsorbents (6, 7); conducting a denitrification treatment on an air having a relatively high pressure or a relatively low temperature; and conducting nitrogen enrichment on an air having a relatively low pressure or a relatively high temperature, preparing a first cylindrical container that is rotatable about a center axis and is disposed inside a tubular body, the first cylindrical container is sandwiched by a second cylindrical container and a third cylindrical container, the second and third cylindrical containers (3, 4) are rotatable about the center axis, wherein the first cylindrical container contains a nitrogen-absorbing adsorbent having a nitrogen adsorption that increases with an increase in pressure or a decrease in temperature, the second cylindrical container contains a moisture-absorbing adsorbent and the third cylindrical container contains a moisture-absorbing adsorbent, wherein the moisture-absorbing adsorbents (6, 7) are disposed at the two sides of the nitrogen-absorbing adsorbent; supplying dry airs having different pressures and temperatures to the nitrogen-absorbing adsorbent, the dry airs being supplied to the nitrogen-absorbing adsorbent in directions opposite to each other, wherein the dry airs are airs from which moisture has already been removed by the moisture-absorbing adsorbents (6, 7); conducting a denitrification treatment on an air having a relatively high pressure or a relatively low temperature; and conducting nitrogen enrichment on an air having a relatively low pressure or a relatively high temperature, thereby conducting oxygen enrichment on the air having the relatively high pressure or the relatively low temperature.