PURPOSE: To recover not only the sensible heat of the reaction gas but also the heat in a post-treating step of the reaction, by carrying out the heat exchange of a high- temperature char formed in the gasifying reaction with cooling water and the reaction gas in a fluidized bed cooler with cooling water respectively.

CONSTITUTION: Coal in a hopper 2 and a gasifying agent 3, e.g. hydrogen or steam, are fed to a reaction bed 5 of a gasifying furnace 1 and gasified at a high temperature and pressure. Water (cooling water) W from a drum 13 after the heat exchange in a char cooler 6, a fluidized bed cooler 9 and a retreating furnace 22 is passed through risers 24a, 24b and 24c, returned to the drum 13 as a hot water or steam, and expelled from a steam pipe 17 to the outside of the system for reuse.