PURPOSE: To operate a gasifying oven under stabilized conditions without causing changes in load, by detecting the amount of coal supply from mesurements of pressure loss between an outlet of a lock hopper and an inlet of the gasifying oven and thereby adjusting inner pressure of the lock hopper 1 to that of the gasifying oven.

CONSTITUTION: Coal is fed into a gasifying oven 4 from a lock hopper 3 kept at an inner pressure higher than that in the oven 4. Loss of pressure between an outlet of the hopper 3 located in a coal supply pipe 15 and an inlet of the oven 4 is used for adjustment of inner pressure of the hopper 3 to that of the oven 4. Thus, coal is supplied consistently from the hopper 3 to the oven 4 without changes in load of the oven, leading to safe operation of the oven.