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.