PURPOSE: To produce efficiently a combustion gas from solid urban wastes, common wood, etc., by adding simultaneously a straight flame and a downward flame to a material to be gasified.

CONSTITUTION: The apparatus comprises a gas generator 10 in which two types of flames (a straight flame 26 and a downward flame 28) are used in its furnace. A suction zone for produced fuel gas or an injection zone for air is arranged in the middle part of the furnace between the positions of the two types of flames. A device for dissolving the non-fuel part of a waste such as glass and metal slug is provided at the bottom of the gas generator 10. A fuel gas produced by the gasification of materials in the gas generator is condensed and returned to the combustion zone of the furnace of the gas generator, where it is burned.