An air pollution control system comprising: a desulfurization device which removes sulfur oxides in a flue gas generated from a boiler ; a cooler which is provided at the downstream side of the desulfurization device and includes a temperature adjustment means configured to adjust a gas dew point temperature of the flue gas to enlarge a particle diameter of SO 3 mist contained in the flue gas , a mist trapping means that is provided near the top and outlet of the cooler in the gas flow direction and that is configured to trap enlarged SO 3 mist from said flue gas , a CO 2 recovery device which includes a CO 2 absorber bringing CO 2 in the flue gas coming from said mist trapping means into contact with a CO 2 absorbent so as to remove CO 2 therefrom and a regenerator recovering CO 2 by dissociating C02 from the CO 2 absorbent and regenerating the CO 2 absorbent, the temperature adjust means including: a heating unit , which includes a heater configured to heat circulation water , and in the heating unit the heated water is brought into contact with the introduced flue gas to heat the flue gas to a temperature higher by 10°C or more from a flue gas introduction temperature in the heating unit , and a cooling unit , which is provided at a downstream side of the heating unit in the gas flow direction, and includes a heat exchanger configured to cool circulation water , and wherein the cooled water is brought into contact with the flue gas to cool the flue gas coming from the heating unit to a temperature equal to or less than a CO 2 absorber introduction temperature via counterflow direct contact with the cooled water . a desulfurization device which removes sulfur oxides in a flue gas generated from a boiler ; a cooler which is provided at the downstream side of the desulfurization device and includes a temperature adjustment means configured to adjust a gas dew point temperature of the flue gas to enlarge a particle diameter of SO 3 mist contained in the flue gas , a mist trapping means that is provided near the top and outlet of the cooler in the gas flow direction and that is configured to trap enlarged SO 3 mist from said flue gas , a CO 2 recovery device which includes a CO 2 absorber bringing CO 2 in the flue gas coming from said mist trapping means into contact with a CO 2 absorbent so as to remove CO 2 therefrom and a regenerator recovering CO 2 by dissociating C02 from the CO 2 absorbent and regenerating the CO 2 absorbent, the temperature adjust means including: a heating unit , which includes a heater configured to heat circulation water , and in the heating unit the heated water is brought into contact with the introduced flue gas to heat the flue gas to a temperature higher by 10°C or more from a flue gas introduction temperature in the heating unit , and a cooling unit , which is provided at a downstream side of the heating unit in the gas flow direction, and includes a heat exchanger configured to cool circulation water , and wherein the cooled water is brought into contact with the flue gas to cool the flue gas coming from the heating unit to a temperature equal to or less than a CO 2 absorber introduction temperature via counterflow direct contact with the cooled water . a heating unit , which includes a heater configured to heat circulation water , and in the heating unit the heated water is brought into contact with the introduced flue gas to heat the flue gas to a temperature higher by 10°C or more from a flue gas introduction temperature in the heating unit , and a cooling unit , which is provided at a downstream side of the heating unit in the gas flow direction, and includes a heat exchanger configured to cool circulation water , and wherein the cooled water is brought into contact with the flue gas to cool the flue gas coming from the heating unit to a temperature equal to or less than a CO 2 absorber introduction temperature via counterflow direct contact with the cooled water . <EOS>