A fuel gasification system including a gasification furnace including a fluidized bed formed by fluidizing reactant gas for gasifying fuel charged into gasification gas and flammable solid content, a combustion furnace for combustion of the flammable solid content into which the flammable solid content produced in the furnace is introduced together with bed material and that includes a fluidized bed formed by fluidizing reactant gas, a material separator such as hot cyclone that separates bed material from exhaust gas introduced from the combustion furnace, the separated bed material being fed through a downcomer to the gasification furnace, and a tar decomposing mechanism that heats the gasification gas produced in the furnace to decompose tar contained in the gasification gas.