PURPOSE: To raise the degree of utilization of coal and make it possible to operate substantially without using oil gas which is a utility by supplying the produced gas to a burner at the time of starting and circulating to the burner the produced gas which is produced with the supply of coal at minimum at the time of hot banking.

CONSTITUTION: During the time of ordinary operation of coal gasification part of the produced gas is extracted by a circulation channel 14 in order to promote the downward flow of the slag of a coal gasification furnace, and the pressure of the extracted gas is raised by a compressor 10, and then the gas is incinerated with an oxide 7 (oxygen, air, etc.) for burner by a burner 2. After ordinary operation, when the daily start and shut-down are performed, the temperature in the coal gasification furnace 1 drops suddenly and it makes hot banking difficult, because the coal gasification furnace 1 incorporates a membrane wall 23 for generating steam. Under the circumstances a minimum amount of coal 3 is charged through a lock hopper 4 with a coal carrier gas 5 and gasification agent 6 to the coal gasification furnace 1 to gasify, and the produced gas is supplied to the burner 2 through the circulation channel 14 to maintain the hot banking and it is also used for heating the slag tapping section.