An exhaust gas treatment device includes an exhaust gas line where a combustion exhaust gas discharged from a power generation facility flows through, an exhaust gas line where a second combustion exhaust gas discharged from a second power generation facility flows through, exhaust gas exhaust line disposed by branching off from exhaust gas line, discharging a part of combustion exhaust gases as exhaust combustion exhaust gases, a nitrogen oxide removing unit removing nitrogen oxide contained in an integrated combustion exhaust gas that integrates the combustion exhaust gases, an integrated waste heat recovery boiler recovering waste heat from the integrated combustion exhaust gas, and a CO2 recovery unit recovering CO2 contained in the integrated combustion exhaust gas by using CO2 absorbing liquid.