An object of the invention is to enhance gasification efficiency of flammable solid content when high fuel ratio fuel having fixed carbon content in large quantity is to be gasified. A material downcomer 11 for introduction of bed material 10 separated in a material separator 9 and a fuel supply port 21 for introduction of gasification fuel 12 are arranged at one side of a gasification furnace 2; a solid content supply port 19 for supply of flammable solid content 18 and the bed material 10 in the gasification furnace 2 to the combustion furnace 1 is arranged at the other side of the gasification furnace 2. In the gasification furnace 2 and between the one and the other sides of the furnace 2, vertical partition plates 22 are arranged to provide a zigzag curved flow passage 23 with upper and lower turns.