NOVELTY - A package type multistage reactor is provided which increases removing efficiency of organic materials and the total amount of nitrogen and treatment efficiency per unit volume of the multistage reactor by forming a fluidized bed on anoxic/aerobic reactors of the package type multistage reactor.    DETAILED DESCRIPTION - The package type multistage reactor combining the upper part of aerobic fluidized biofilm process and the lower part of anoxic process is characterized in that heterotrophic microorganism denitrification bacteria are fixed to carriers(24) in anoxic tanks(2) that are lower stages of the multistage reactor(1), each of the lower stages are divided by partitions(3) on which holes are perforated, aerobic autotrophic microorganism nitrification bacteria are fixed to the carriers in fluidized bed aerobic tanks(4) that are upper stages of the multistage reactor(1), oxygen is supplied from under the aerobic/anoxic tank partitions(5), the supplied air is split into pieces and dispersed properly as passing through several partitions and being collided with the movable carriers(23), air can be additionally supplied between stages of the fluidized bed aerobic tanks(4) for additional aeration, a stage(25) in which carriers are not filled is formed on the upper part of the multistage reactor(1), an air hole(7) is installed on the top of the stage(25), effluent overflows a weir(8) and is supplied into a settling tank(10) through an outlet(9), some of the effluent comes out of the settling tank(10) as advanced treated raw water(12) after a certain period of retention time while a balance of the effluent is recirculated to be mixed with inflow sewage and wastewater(14) by a circulation pump(13) so that the mixture is flown into an inflow port(15) at the lower part of the anoxic tanks(2), a thermostat water bath(16) is installed on the outer wall of the multistage reactor(1), hot water is flown into a hot water inlet(17) and discharged from a hot water outlet(18) as passing through the thermostat water bath(16), an inclined plate(20) the central part of which is slanted downward is installed on the bottom of the lower part of the anoxic tanks(2) to easily discharge sludge, sewage and wastewater under the anoxic condition is recirculated from the upper part to the bottom of the lower part of the anoxic tanks(2) when forming the anoxic tanks(2) in a fluidized bed, and a counter-current preventing plate(22) is installed on the upper part of the anoxic tanks(2).