To prevent the dew point corrosion by conversion of the combustion exhaustion gas to drain on the start-up of the plant and stabilize the start-up operation to shorten the start-up time.

In this coal produced gas generator, the oxidizer is used to form the produced gas from coal 20, the heat of the produced gas is recovered in the heat-recovery boiler 2 and the unreacting char and the dust are removed with the cyclone 3 and the dust filter 4 to prepare the crude produced gas. The crude produced gas is washed with the water-washing column 7, cooled down and desulfurized with the wet-type desulfurizer 10 to prepare the purified gas 30 and the purified fuel gas is used to increase the temperature and the pressure on the start-up. Thus, as a fuel for start-up, is used a fuel gas 32 other than hydrogen that is stored in the holder 13 after removal of hydrogen and moisture from the purified gas 30.