NOVELTY - The double fluidized bed reactor comprises: a top body equipped with a sedimentation tank and an uprising pipe arranged in a longitudinal direction from a lower end portion of the top body; a central body equipped with a combustion space into which the pipe is inserted; and a lower body equipped with a combustion air tank. The reactor further comprises a material inlet into which the raw material is inputted, a unit for supplying a gasification agent to the inlet, a synthetic gas vent for ejecting the produced synthetic gas from top of the top body, and a spreader plate.    USE - The double fluidized bed reactor is useful for indirect gasification of raw materials such as natural gas, biomass and coal of petrochemical product.    ADVANTAGE - The reactor efficiently performs indirect gasification of raw materials, while preventing thermal expansion due to high temperature and preventing mechanical problem occurring due to the expansion of the hot spot.    DETAILED DESCRIPTION - The double fluidized bed reactor comprises: a top body equipped with a sedimentation tank and an uprising pipe arranged in a longitudinal direction from a lower end portion of the top body; a central body equipped with a combustion space into which the pipe is inserted; and a lower body equipped with a combustion air tank. The reactor further comprises a material inlet into which the raw material is inputted, a unit for supplying a gasification agent to the inlet, a synthetic gas vent for ejecting the produced synthetic gas from top of the top body, and a spreader plate. The top body comprises an upper cover portion and a funnel part. The cover portion covers the upper portion of the funnel part. The cover portion and the funnel part are coupled to the central body through a flange coupling. A distribution plate is arranged between the central body and the lower body. The spreader plate includes a nozzle for supplying combustion air to the combustion space. The uprising pipe is protruded to the upper portion from the funnel part. A clamping board is connected to the spreader plate. A lower cover portion is installed in a lower part of the lower body.