PURPOSE: To improve thermal efficiency eliminating a steam cycle having low efficiency by providing a primary combustor system in which air etc. is pressure- risen with a compressor to be high-temperature-burnt together with coal, and a secondary combustor system in which a generated gas in the primary combustor system, oxygen, and vapor are completely burnt.

CONSTITUTION: Coal is supplied from a supply tube 8 to the primary combustor 2 of a primary combustor system A. Meantime, air is separated with an air separator 9, and oxygen, after nitrogen is separated, is supplied to a compressor 1 via an oxygen gas holder 10, then supplied as a cooling fluid for a primary combustion gas cooler 13 to lower the temperature of a high-temperature burnt gas generated in the primary combustor 2 to a temperature required from a dust remover 14. A primary combustion gas is supplied to the secondary combustor 3 of a secondary combustor system B via the dust remover 14. Moreover a gas turbine 4 is driven by a secondary combustion gas, and then a gas turbine exhaust gas is sent to an exhaust heat recovery steam generator 5, desulfurizer 6, and exhaust gas condenser 7.