PURPOSE: To provide synthesis gas by gasifying a carbonaceous material of granulated coal, mixing the synthesis gas with ash produced at the gasification, cooling the mixture, and separating the gas from ash to be used for the driving of a gas turbine to solve the problems on contamination and attachment.

CONSTITUTION: The carbonaceous fuel of granulated coal is introduced into a gasifier 10 from a conduit 13, and oxygen and steam are introduced into the gasifier 10 respectively through the conduits 12, 14 to gasify coal. A mixture product including a large amount of ash at the gasification is guided to a separator 24 through an entrained matter container 20 and a duct 22. The mixture is cooled by cooling water passing in a tube bundle 25, and the heated water or steam is supplied to a steam turbine 26. On the other hand, the synthesis gas is supplied to a heat exchanger 30 through a duct 29, the particles are supplied to a heat exchanger 50 through a duct 49, and the separated particles in the heat exchanger 50 are cooled by the water passing in a flow circuit connected to the steam turbine 26, and then supplied inside of the entrained matter container 20 through the branched ducts 52a-52c to be utilized for cooling the mixture.