NOVELTY - The reactor comprises a first reaction container including a gas trap portion in a lower portion and an inflow water inlet port in an upper portion. A first microorganism support is fixed to an inner portion of the first reaction container. A second reaction container includes a vent in an upper portion and a through-hole in a lower portion. An anode collector, an anode, an electrolyte film, a cathode and a cathode current collector are serially arranged in the through-hole within the second reaction container. A second microorganism support is fixed on the anode.    USE - The reactor is useful in a microbial fuel cell system for processing an organic compound to produce electricity and biogas.    ADVANTAGE - The reactor treats the organic compound in an inexpensive manner, and improves the productivity of electric power and biogas.    DETAILED DESCRIPTION - The reactor comprises a first reaction container including a gas trap portion in a lower portion and an inflow water inlet port in an upper portion. A first microorganism support is fixed to an inner portion of the first reaction container. A second reaction container includes a vent in an upper portion and a through-hole in a lower portion. An anode collector, an anode, an electrolyte film, a cathode and a cathode current collector are serially arranged in the through-hole within the second reaction container. A second microorganism support is fixed on the anode. The second reaction container surrounds the first reaction container, where the first reaction container is in a cylindrical or columnar structure, and the second reaction container is in a columnar structure. The second reaction container includes a set of sub reaction containers that are combined in a stacked structure form top to bottom. The through-hole is formed in sides of the second reaction container. The first reaction container is filled with a granular sludge and a filler, where an average diameter of each of the particles of the granular sludge is 1-3 mm. The inflow water movement to the second reaction container is performed in the first reaction container with a non-power natural falling mode. The reactions of the first and second reaction containers are performed in an anaerobic condition. The reactor further comprises a unit for removing a nitrogen source from the inflow water before the water flows into the first reaction container. The second reaction container is provided with a temperature controller.