A circulating-type multi-layer furnace comprising: a circulation unit adapted for incinerating a sludge while feeding an air circulating a flowing medium; a post-combustion unit adapted for feeding an air to a thermal decomposition gas from the circulation unit to conduct a perfect combustion, wherein the circulating-type multi-layer furnace is adapted to: conduct a first control in which an air in an air flow amount being required for the perfect combustion and corresponding to an injected sludge amount is fed to the circulation unit and the post-combustion unit separately at a predetermined ratio, wherein the circulating-type multi-layer furnace is adapted to: conduct a second control in which, in a case where an air flow amount of the air to be fed to the circulation unit is lower than an air flow amount required for circulating the flowing medium in the first control, an air equal to or larger than a minimum air flow amount required for circulating the flowing medium in the circulation unit, of the air in the air flow amount required for the perfect combustion is fed to the circulation unit and a remaining amount of the air in the air flow amount required for the perfect combustion is fed to the post-combustion unit. a circulation unit adapted for incinerating a sludge while feeding an air circulating a flowing medium; a post-combustion unit adapted for feeding an air to a thermal decomposition gas from the circulation unit to conduct a perfect combustion, wherein the circulating-type multi-layer furnace is adapted to: conduct a first control in which an air in an air flow amount being required for the perfect combustion and corresponding to an injected sludge amount is fed to the circulation unit and the post-combustion unit separately at a predetermined ratio, wherein the circulating-type multi-layer furnace is adapted to: conduct a second control in which, in a case where an air flow amount of the air to be fed to the circulation unit is lower than an air flow amount required for circulating the flowing medium in the first control, an air equal to or larger than a minimum air flow amount required for circulating the flowing medium in the circulation unit, of the air in the air flow amount required for the perfect combustion is fed to the circulation unit and a remaining amount of the air in the air flow amount required for the perfect combustion is fed to the post-combustion unit. conduct a first control in which an air in an air flow amount being required for the perfect combustion and corresponding to an injected sludge amount is fed to the circulation unit and the post-combustion unit separately at a predetermined ratio, wherein the circulating-type multi-layer furnace is adapted to: conduct a second control in which, in a case where an air flow amount of the air to be fed to the circulation unit is lower than an air flow amount required for circulating the flowing medium in the first control, an air equal to or larger than a minimum air flow amount required for circulating the flowing medium in the circulation unit, of the air in the air flow amount required for the perfect combustion is fed to the circulation unit and a remaining amount of the air in the air flow amount required for the perfect combustion is fed to the post-combustion unit.