To provide a metallic carbonizing furnace which is operated easily.

Spontaneous carbonization heat of a carbonizable material W with a high water content is conducted directly to a heating smoke exhaustion duct 8 provided in the middle of the carbonizing furnace 1 to heat flue gas within the heating smoke exhaustion duct 8. By doing so, strong draft is generated and the flue gas is discharged forcibly to the outside of the furnace. At the same time, fresh air is supplied forcibly to the carbonizable material W to continue heat generation. In order to complete carbonization of the dry carbonizable material W in a short time in the metallic carbonizing furnace 1, an insertion connecting concave part 8a for the heating smoke exhaustion duct is removed as a removable connecting attachment 8c for the heating smoke exhaustion duct and a heating smoke exhaustion duct cap 8d is mounted. By doing so, combustion gas and carbonized wood gas are discharged directly to a chimney 2a from a small gap formed by removing the attachment.