To reduce manufacturing cost and operating cost of a burner while suppressing generation of hexavalent chrome in combustion ash.

By changing a combustion cylinder constituting a combustion chamber of the woody pellet burning gun type burner from an air cooling type to a water cooling type, use materials are changed and accessary apparatuses are reduced. Since a reheating chamber lined by a refractory heat insulating material is provided immediately downstream of the combustion chamber to perform further complete combustion of unburned back ash made to flow from the burner combustion chamber, use efficiency of fuel can be improved and cost of the device and the operating cost can be reduced.