NOVELTY - The fluidized bed reactor comprises a reactor body, a distribution plate mounted on the reactor body, and a projecting structure formed on an inner portion of the reactor body. The projecting structure has an annular structure, a longitudinal structure, a triangular structure, a trapezoidal structure, a semi-spherical structure or a semi-elliptical structure. The fluidized bed reactor further comprises a supply pipe for supplying a catalyst into the reactor body, a carbon source connected to a bottom portion of the reactor body, and a gas supply pipe.    USE - The fluidized bed reactor is useful for manufacturing carbon nanostructures (claimed) such as carbon nanotubes and carbon nanofibers, which are useful in a secondary battery, an electrode of a electrochemical storage unit such as fuel cell or super capacitor, a field emission display and a gas sensor and for electromagnetic interference shielding.    ADVANTAGE - The reliable fluidized bed reactor manufactures the carbon nanostructures with improved quality and productivity.    DETAILED DESCRIPTION - The fluidized bed reactor comprises a reactor body, a distribution plate mounted on the reactor body, and a projecting structure formed on an inner portion of the reactor body. The projecting structure has an annular structure, a longitudinal structure, a triangular structure, a trapezoidal structure, a semi-spherical structure or a semi-elliptical structure. The fluidized bed reactor further comprises a supply pipe for supplying a catalyst into the reactor body, a carbon source connected to a bottom portion of the reactor body, and a gas supply pipe for supplying a reaction gas containing a reducing gas and an inert gas into the reactor body, where the catalyst and the reaction gas are reacted inside the reactor body to produce a carbon nanostructure. An aperture ratio of the projecting structure is greater than the aperture ratio of the distribution plate. An INDEPENDENT CLAIM is included for a method for manufacturing a carbon nanostructure.