A plant comprising a combustion facility having a boiler that discharges flue gas to a flue gas duct, that heats condensed water from a condensed water line and that discharges steam to a steam extracting line, the combustion facility having turbines that acquire rotative power by superheated steam from the boiler; an air/flue gas heat exchanger that performs heat exchange between the flue gas and combustion air, a desulfurizer that reduces sulfur content contained in flue gas in the flue gas duct; a CO 2 recovery unit including: an absorber that reduces CO 2 in flue gas discharged from a combustion facility by absorbing CO 2 by an absorbent; a regenerator that heats the absorbent having absorbed CO 2 to emit CO 2, and regenerates and supplies the absorbent to the absorber; a regenerating heater that uses steam supplied from the steam extracting line for heating the absorbent in the regenerator and returns heated condensed water to the combustion facility via the condensed water line; and a condensed water/flue gas heat exchanger that heats condensed water of the condensed water line to be returned from the regenerating heater to the combustion facility by heat-exchanging the condensed water with flue gas in the flue gas duct discharged from the air/flue gas heat exchanger, wherein the air/flue gas heat exchanger is provided upstream of the condensed water/flue gas heat exchanger in the flue gas duct and wherein a condensed water/flue gas heat exchanging line for heat-exchanging between condensed water and flue gas is provided in middle of the condensed water line, and a bypass line for directly connecting the condensed water line without via the condensed water/flue gas heat exchanging line is provided. a combustion facility having a boiler that discharges flue gas to a flue gas duct, that heats condensed water from a condensed water line and that discharges steam to a steam extracting line, the combustion facility having turbines that acquire rotative power by superheated steam from the boiler; an air/flue gas heat exchanger that performs heat exchange between the flue gas and combustion air, a desulfurizer that reduces sulfur content contained in flue gas in the flue gas duct; a CO 2 recovery unit including: an absorber that reduces CO 2 in flue gas discharged from a combustion facility by absorbing CO 2 by an absorbent; a regenerator that heats the absorbent having absorbed CO 2 to emit CO 2, and regenerates and supplies the absorbent to the absorber; a regenerating heater that uses steam supplied from the steam extracting line for heating the absorbent in the regenerator and returns heated condensed water to the combustion facility via the condensed water line; and a condensed water/flue gas heat exchanger that heats condensed water of the condensed water line to be returned from the regenerating heater to the combustion facility by heat-exchanging the condensed water with flue gas in the flue gas duct discharged from the air/flue gas heat exchanger, wherein the air/flue gas heat exchanger is provided upstream of the condensed water/flue gas heat exchanger in the flue gas duct and wherein a condensed water/flue gas heat exchanging line for heat-exchanging between condensed water and flue gas is provided in middle of the condensed water line, and a bypass line for directly connecting the condensed water line without via the condensed water/flue gas heat exchanging line is provided. an absorber that reduces CO 2 in flue gas discharged from a combustion facility by absorbing CO 2 by an absorbent; a regenerator that heats the absorbent having absorbed CO 2 to emit CO 2, and regenerates and supplies the absorbent to the absorber; a regenerating heater that uses steam supplied from the steam extracting line for heating the absorbent in the regenerator and returns heated condensed water to the combustion facility via the condensed water line; and a condensed water/flue gas heat exchanger that heats condensed water of the condensed water line to be returned from the regenerating heater to the combustion facility by heat-exchanging the condensed water with flue gas in the flue gas duct discharged from the air/flue gas heat exchanger, wherein the air/flue gas heat exchanger is provided upstream of the condensed water/flue gas heat exchanger in the flue gas duct and wherein a condensed water/flue gas heat exchanging line for heat-exchanging between condensed water and flue gas is provided in middle of the condensed water line, and a bypass line for directly connecting the condensed water line without via the condensed water/flue gas heat exchanging line is provided.