To permit the always stable start-up of a coal gasifier while preventing dew point corrosion by a waste combustion gas during start-up by using charr as a fuel for starting up a coal gasifier.

Air 57 is sucked in and is separated into oxygen 18 and nitrogen in a rectifying tower 1, and the both are respectively transferred to an oxygen compressor 21 and a nitrogen compressor 23. After the pilot burner inside a coal gasifier 5 is ignited, the charr loaded on a charr feed hopper 11 is transferred to a charr burner by entrainment on nitrogen 20 through a pipe and is burnt with oxygen transferred to the burner. After the temperatures of the respective sections of the plant are raised to ones at which the moisture generated during coal gasification is not condensed, the coal 4 in a coal feed hopper 3 is fed into the gasifier 5 to start gasification. The charr burner is extinguished. The charr 12 produced by the gasification of coal is collected in a deduster 9 and stored as a start-up fuel in the hopper 11.