An apparatus which includes a fuel feeder (3), an oxygen separator (6), an air feeder (7), a combustion furnace (11) in which a fuel is burned with a burner (9), a combustion gas line (14) which leads the combustion gas resulting from the burning in the combustion furnace (11) to the outside of the combustion furnace (11), combustion gas treatment means (20a) and (20b) disposed in the combustion gas line (14), and a recycle line (15) through which part of the combustion gas having at least undergone a dust removal treatment with the combustion gas treatment means (20a) and (20b) is recycled to the burner (9). It further has: a combustion gas recovery means (18) which takes carbon dioxide out of the remaining combustion gas which is not recycled; and carbon dioxide feeders (33), (40), and (46) which introduce carbon dioxide respectively into a device (10) and the means (20a) and (20b) in the oxygen combustion boiler apparatus.