Provided are high-pressure, medium-pressure, and low-pressure turbines; a boiler (15) to generate steam for driving the turbines; a carbon dioxide recovery unit including an absorber (18) that reduces carbon dioxide in combustion flue gas from the boiler (15) by means of a carbon dioxide absorbent and a regenerator that regenerates an absorbent; a first auxiliary turbine (22L) that extracts steam from an inlet of the low-pressure turbine and recovers power by means of the steam thus extracted; a first steam delivery line to supply discharged steam from the first auxiliary turbine (22L) to a reboiler (24) of the regenerator as a heat source; and a controller that controls driving of the first auxiliary turbine (22L) while keeping pressure of the discharged steam to be supplied to the reboiler (24) within a tolerance range for the optimum pressure of the reboiler (24) corresponding to a fluctuation in an operation load of the boiler (15).
