To increase a throughput of materials to be treated per one carbonization furnace.

The carbonization furnace is equipped with two or more groups 11, 11' of inner furnaces and a movable outer furnace 20. The groups 11, 11' of inner furnaces comprise two or more inner furnaces 10, 10'. The inner furnaces 10, 10' have inner furnace lids 12, 12' to be opened and closed. The movable outer furnace 20 has an opening end 21 and freely moves between the groups 11, 11' of inner furnaces. The movable outer furnace 20 takes either one of the groups 11 or 11' of inner furnaces from the opening end 21 into inside and forms a combustion chamber between the movable outer furnace 20 and the outer surface of the inner furnace 10 or 10'. The material to be treated carried into the inner furnace 10 is carbonized by burning a burner or the like in the combustion chamber.