A gas separation device comprising: an adsorption tower, at least part of the adsorption tower being exposed to an atmosphere at a temperature higher or lower than a normal temperature; a mixed gas feed unit configured to feed a mixed gas, which contains a plurality of substances, into the adsorption tower from one end or another end of the adsorption tower; an adsorbent disposed in the adsorption tower such that when the adsorbent contacts the mixed gas in a prescribed pressure and temperature environment, the adsorbent adsorbs a substance contained in the mixed gas to separate the substance from the mixed gas; a separated gas discharge unit configured to discharge a separated gas from said one end or said another end of the adsorption tower, the separated gas being produced from the mixed gas upon separation of the substance adsorbed by the adsorbent from the mixed gas; an adsorbed gas discharge unit configured to reduce an inner pressure of the adsorption tower and cause an adsorbed gas, which is adsorbed by the adsorbent, to desorb from the adsorbent so as to discharge the adsorbed gas from an interior of the adsorption tower; heat reserving elements disposed upstream and downstream of the adsorbent in a mixed gas feeding direction such that the mixed gas supplied into the adsorption tower from the mixed gas feed unit, the separated gas discharged from the interior of the adsorption tower by the separated gas discharge unit, and the adsorbed gas discharged from the interior of the adsorption tower by the adsorbed gas discharge unit pass through the heat reserving elements, the heat reserving elements being configured to reduce an outflow of heat to outside from the adsorbent and an inflow of heat to the adsorbent from the outside; and a control unit configured to control a gas separation process that sequentially carries out a feed process of controlling the mixed gas feed unit to feed the mixed gas into the adsorption tower, a separated gas discharge process of controlling the separated gas discharge unit to discharge the separated gas from the interior of the adsorption tower, and an adsorbed gas discharge process of controlling the adsorbed gas discharge unit to discharge the adsorbed gas from the interior of the adsorption tower, the control unit being configured to control the mixed gas feed unit during the feed process such that the mixed gas is fed from that end of the adsorption tower, among said one end and said another end of the adsorption tower, from which the separated gas is discharged in a preceding separated gas discharge process, and the control unit being configured to control the separated gas discharge unit during the separated gas discharge process such that the separated gas is discharged from that end of the adsorption tower which is different from the end used to discharge the separated gas in the preceding separated gas discharge process. an adsorption tower, at least part of the adsorption tower being exposed to an atmosphere at a temperature higher or lower than a normal temperature; a mixed gas feed unit configured to feed a mixed gas, which contains a plurality of substances, into the adsorption tower from one end or another end of the adsorption tower; an adsorbent disposed in the adsorption tower such that when the adsorbent contacts the mixed gas in a prescribed pressure and temperature environment, the adsorbent adsorbs a substance contained in the mixed gas to separate the substance from the mixed gas; a separated gas discharge unit configured to discharge a separated gas from said one end or said another end of the adsorption tower, the separated gas being produced from the mixed gas upon separation of the substance adsorbed by the adsorbent from the mixed gas; an adsorbed gas discharge unit configured to reduce an inner pressure of the adsorption tower and cause an adsorbed gas, which is adsorbed by the adsorbent, to desorb from the adsorbent so as to discharge the adsorbed gas from an interior of the adsorption tower; heat reserving elements disposed upstream and downstream of the adsorbent in a mixed gas feeding direction such that the mixed gas supplied into the adsorption tower from the mixed gas feed unit, the separated gas discharged from the interior of the adsorption tower by the separated gas discharge unit, and the adsorbed gas discharged from the interior of the adsorption tower by the adsorbed gas discharge unit pass through the heat reserving elements, the heat reserving elements being configured to reduce an outflow of heat to outside from the adsorbent and an inflow of heat to the adsorbent from the outside; and a control unit configured to control a gas separation process that sequentially carries out a feed process of controlling the mixed gas feed unit to feed the mixed gas into the adsorption tower, a separated gas discharge process of controlling the separated gas discharge unit to discharge the separated gas from the interior of the adsorption tower, and an adsorbed gas discharge process of controlling the adsorbed gas discharge unit to discharge the adsorbed gas from the interior of the adsorption tower,