An exhaust gas treatment device (1, 2, 3, 4) comprising: a first exhaust gas flow path (L 11-1) where a first combustion exhaust gas (G 11-1) discharged from a first power generation facility flows through; a second exhaust gas flow path (L 11-2) where a second combustion exhaust gas (G 11-2) discharged from a second power generation facility flows through; an exhaust gas exhaust flow path (L 12-1) (L 12-2) disposed by branching off from each of the first exhaust gas flow path (L 11-1) and the second exhaust gas flow path (L 11-2), and configured to discharge an exhaust combustion exhaust gas to outside, the exhaust combustion exhaust gas including at least a part of each of the first combustion exhaust gas (G 11-1) flowing through the first exhaust gas flow path (L 11-1) and the second combustion exhaust gas (G 11-2) flowing through the second exhaust gas flow path (L 11-2); a nitrogen oxide removing unit configured to remove nitrogen oxide contained in an integrated combustion exhaust gas obtained by integrating the first combustion exhaust gas (G 11-1) from the first exhaust gas flow path (L 11-1) with the second combustion exhaust gas (G 11-2) from the second exhaust gas flow path (L 11-2); an integrated waste heat recovery unit configured to recover waste heat from the integrated combustion exhaust gas with nitrogen oxide removed by the nitrogen oxide removing unit; and a CO 2 recovery unit configured to recover CO 2 contained in the integrated combustion exhaust gas by using CO 2 absorbing liquid, the exhaust gas exhaust flow paths (L 12-1) (L 12-2) being branched off between the first power generation facility or the second power generation facility and the nitrogen oxide removing unit; the exhaust gas treatment device (1, 2, 3, 4) further comprising a control unit configured to control a flow rate of the first combustion exhaust gas (G 11-1) and the second combustion exhaust gas (G 11-2) both introduced to the integrated waste heat recovery unit. a first exhaust gas flow path (L 11-1) where a first combustion exhaust gas (G 11-1) discharged from a first power generation facility flows through; a second exhaust gas flow path (L 11-2) where a second combustion exhaust gas (G 11-2) discharged from a second power generation facility flows through; an exhaust gas exhaust flow path (L 12-1) (L 12-2) disposed by branching off from each of the first exhaust gas flow path (L 11-1) and the second exhaust gas flow path (L 11-2), and configured to discharge an exhaust combustion exhaust gas to outside, the exhaust combustion exhaust gas including at least a part of each of the first combustion exhaust gas (G 11-1) flowing through the first exhaust gas flow path (L 11-1) and the second combustion exhaust gas (G 11-2) flowing through the second exhaust gas flow path (L 11-2); a nitrogen oxide removing unit configured to remove nitrogen oxide contained in an integrated combustion exhaust gas obtained by integrating the first combustion exhaust gas (G 11-1) from the first exhaust gas flow path (L 11-1) with the second combustion exhaust gas (G 11-2) from the second exhaust gas flow path (L 11-2); an integrated waste heat recovery unit configured to recover waste heat from the integrated combustion exhaust gas with nitrogen oxide removed by the nitrogen oxide removing unit; and a CO 2 recovery unit configured to recover CO 2 contained in the integrated combustion exhaust gas by using CO 2 absorbing liquid, the exhaust gas exhaust flow paths (L 12-1) (L 12-2) being branched off between the first power generation facility or the second power generation facility and the nitrogen oxide removing unit; the exhaust gas treatment device (1, 2, 3, 4) further comprising a control unit configured to control a flow rate of the first combustion exhaust gas (G 11-1) and the second combustion exhaust gas (G 11-2) both introduced to the integrated waste heat recovery unit.