SOx removal equipment 15 which reduces sulfur oxides from flue gas 12 from a boiler 11, a cooler 16 which is provided on the downstream side of the SOx removal equipment 15 so as to reduce the sulfur oxides from the flue gas and decrease a gas temperature, CO2 recovery equipment 17 which includes an absorber for bringing CO2 in the flue gas into contact with a CO2 absorption liquid so as to be reduced and a regenerator for causing the CO2 absorption liquid to emit CO2 so as to recover CO2 and regenerate the CO2 absorption liquid, and ammonia injection equipment 22 for reducing a mist generation material which is a generation source of mist that is generated in the absorber of the CO2 recovery equipment before introducing the flue gas to the CO2 recovery equipment, are included.