A gasification system comprising: a gasification furnace configured to gasify fuel; a fuel supply apparatus configured to supply fuel to the gasification furnace; and an inner cylinder configured to introduce the fuel and air into the gasification furnace, the inner cylinder being included in the gasification furnace; wherein a height from a lower end opening in the inner cylinder to a predetermined height position is set as an inside furnace level target value, and an inside furnace level upper limit (Hh) is set, wherein the gasification system further includes: a fuel detection unit (25, 26, 27) configured to detect, as an inside furnace level, an accumulated height of the fuel accumulated inside the inner cylinder; and a control apparatus configured to determine the inside furnace level and control the fuel supply apparatus, wherein, when the inside furnace level is determined to be equal to or higher than the inside furnace level upper limit (Hh), the fuel supply apparatus is stopped, and when the inside furnace level is determined to be lower than the inside furnace level upper limit (Hh), a deviation (ΔH) between the inside furnace level target value and the inside furnace level is obtained and the fuel supply apparatus is controlled according to the deviation ΔH so that the inside furnace level is coincident with the inside furnace level target value. a gasification furnace configured to gasify fuel; a fuel supply apparatus configured to supply fuel to the gasification furnace; and an inner cylinder configured to introduce the fuel and air into the gasification furnace, the inner cylinder being included in the gasification furnace; wherein a height from a lower end opening in the inner cylinder to a predetermined height position is set as an inside furnace level target value, and an inside furnace level upper limit (Hh) is set, wherein the gasification system further includes: a fuel detection unit (25, 26, 27) configured to detect, as an inside furnace level, an accumulated height of the fuel accumulated inside the inner cylinder; and a control apparatus configured to determine the inside furnace level and control the fuel supply apparatus, wherein, when the inside furnace level is determined to be equal to or higher than the inside furnace level upper limit (Hh), the fuel supply apparatus is stopped, and when the inside furnace level is determined to be lower than the inside furnace level upper limit (Hh), a deviation (ΔH) between the inside furnace level target value and the inside furnace level is obtained and the fuel supply apparatus is controlled according to the deviation ΔH so that the inside furnace level is coincident with the inside furnace level target value. a fuel detection unit (25, 26, 27) configured to detect, as an inside furnace level, an accumulated height of the fuel accumulated inside the inner cylinder; and a control apparatus configured to determine the inside furnace level and control the fuel supply apparatus, wherein, when the inside furnace level is determined to be equal to or higher than the inside furnace level upper limit (Hh), the fuel supply apparatus is stopped, and when the inside furnace level is determined to be lower than the inside furnace level upper limit (Hh), a deviation (ΔH) between the inside furnace level target value and the inside furnace level is obtained and the fuel supply apparatus is controlled according to the deviation ΔH so that the inside furnace level is coincident with the inside furnace level target value.