NOVELTY - The fuel cell utilizing biogas as a fuel, is claimed. The fuel cell is supplied with a first gas required at a fuel electrode (111) and a second gas required at an air electrode (112). The first gas and the second gas are separated from the biogas by a gas-purification separation unit. The fuel cell supplies a gas discharged from the fuel electrode, along with the biogas, to the gas-purification separation unit. The biogas is separated using a separation membrane of the gas-purification separation unit by a selective permeation method.    USE - The fuel cell (such as molten carbonate fuel cell, polymer electrolyte membrane fuel cell, solid oxide fuel cell, direct methanol fuel cell, direct ethanol fuel cell and phosphoric acid fuel cell) is useful for generating electrical energy.    ADVANTAGE - The fuel cell has improved stability, service life and heat efficiency, and prevents loss of surplus heat.    DETAILED DESCRIPTION - The fuel cell utilizing biogas as a fuel, is claimed. The fuel cell is supplied with a first gas required at a fuel electrode (111) and a second gas required at an air electrode (112). The first gas and the second gas are separated from the biogas by a gas-purification separation unit. The fuel cell supplies a gas discharged from the fuel electrode, along with the biogas, to the gas-purification separation unit. The biogas is separated using a separation membrane of the gas-purification separation unit by a selective permeation method. The fuel cell further supplies gas discharged from the air electrode to a polisher (120) such that the gas is subjected to hydrogenation reaction with the biogas to increase a purity of methane in the biogas. The fuel cell is re-supplied with unreacted hydrogen gas from the polisher. The biogas is an anaerobic digestion gas. The fuel cell provides the gas at a high temperature, which is discharged from the fuel cell when sludge is dried and/or digested. The fuel cell further comprises a pre-reforming unit to convert hydrocarbon into hydrogen at a front end of the fuel cell, and a unit to mix the first gas with natural gas at a front end of the pre-reforming unit to supply the mixture to the pre-reforming unit. The gas-purification separation unit is supplied with the biogas that is purified by a pre-treatment system. The pre-treatment system removes one of sulfur compounds, moisture and siloxane from the biogas. An INDEPENDENT CLAIM is included for a method for generation of electrical energy using a fuel cell.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a fuel cell.    Fuel electrode (111)    Air electrode (112)    Oxidation unit (113)    Polisher (120)    Dewatering apparatus. (220)