PURPOSE: To promote the gasification of fuel and prevent the clogging of a pipe to make a stable combustion by a method wherein a gasification pipe in which a pipe wall is made in the shape of a spiral irregular surface is wound around the outer circumference of the combustion cylinder.

CONSTITUTION: Pipe wall 30 of the gasification pipe 6 is formed with a spiral projection 31. Wall of the combustion cylinder 2 is heated by a combustion, the gasification pipe 6 is heated by the discharged heat, while the fuel flowed in the gasification pipe 6 is gasified and injected out from the nozzle 21 for the gasified fuel. In this way, the pipe having a spiral irregular shaped wall is used as the gasification pipe, a wide thermal conducting area is obtained and a gasification of the fuel is improved or promoted. Even if the carbide or tar is adhered to the pipe, they are adhered only to the large diametered part, so that the pipe may not be clogged and a stable supplying of fuel may be performed.