A condensate treatment system for a thermal power plant or a nuclear power plant, for removing suspended impurities and ionic impurities from condensate, comprising: a vessel in a form of a body of revolution; a hollow columnar body (40, 240) that is located in an internal space of the vessel, one end of the columnar body being connected to an inner surface of the vessel along an entire circumference of the end, and the other end of the columnar body forming an opening; and a partition plate (44, 244) that is connected to the other end of the hollow columnar body along an entire circumference of the other end, the partition plate (44, 244) being configured to separate an inside space (41, 241) or an outside space of the hollow columnar body (40, 240) as an independent space in the vessel, wherein the partition plate (44, 244) has a circulation port (43, 243) that allows water that is to be treated to pass therethrough, and wherein the independent space (41, 241) in the vessel that is separated by the partition plate (44, 244) is a filtration chamber (41, 241) in which filter elements (42, 242) are loaded, and the inside space or the outside space of the hollow columnar body (40, 240) that is not separated as the independent space by the partition plate (44, 244) is a demineralization chamber containing ion exchangers, the water that was treated in the filtration chamber (41, 241) is adapted to enter the demineralization chamber through the circulation port (43, 243), further comprising; a line (146, 141, 46) that connects an outlet of water that is treated with an inlet of water that is to be treated, the outlet being located at the demineralization chamber and the inlet being located at the filtration chamber (41, 241); a pump that is provided on the line (146, 141, 46), the pump being configured to circulate water that exits from the outlet of the demineralization chamber to the inlet of the filtration chamber (41, 241); an air supply port for backwashing the ion exchangers, the air supply port being located below a layer of charged ion exchangers in the demineralization chamber, and an air discharge port for discharging air that was supplied, the air discharge port being located at a top of the vessel. a vessel in a form of a body of revolution; a hollow columnar body (40, 240) that is located in an internal space of the vessel, one end of the columnar body being connected to an inner surface of the vessel along an entire circumference of the end, and the other end of the columnar body forming an opening; and a partition plate (44, 244) that is connected to the other end of the hollow columnar body along an entire circumference of the other end, the partition plate (44, 244) being configured to separate an inside space (41, 241) or an outside space of the hollow columnar body (40, 240) as an independent space in the vessel, wherein the partition plate (44, 244) has a circulation port (43, 243) that allows water that is to be treated to pass therethrough, and wherein the independent space (41, 241) in the vessel that is separated by the partition plate (44, 244) is a filtration chamber (41, 241) in which filter elements (42, 242) are loaded, and the inside space or the outside space of the hollow columnar body (40, 240) that is not separated as the independent space by the partition plate (44, 244) is a demineralization chamber containing ion exchangers, the water that was treated in the filtration chamber (41, 241) is adapted to enter the demineralization chamber through the circulation port (43, 243), further comprising; a line (146, 141, 46) that connects an outlet of water that is treated with an inlet of water that is to be treated, the outlet being located at the demineralization chamber and the inlet being located at the filtration chamber (41, 241); a pump that is provided on the line (146, 141, 46), the pump being configured to circulate water that exits from the outlet of the demineralization chamber to the inlet of the filtration chamber (41, 241); an air supply port for backwashing the ion exchangers, the air supply port being located below a layer of charged ion exchangers in the demineralization chamber, and an air discharge port for discharging air that was supplied, the air discharge port being located at a top of the vessel.