Provided is a combustion improvement method for an incinerator in a complex facility, wherein biogas produced in a fermenter can be effectively used, and slow combustion can be performed to improve combustion and reduce the production of CO and NOx by feeding the combustion exhaust gas of the biogas into a combustion chamber to which an incinerator stoker is provided. A combustion improvement method for an incinerator (17) in a complex facility (11) comprising a fermenter (12) for fermenting a biogas, a combustor (15) for combusting the biogas produced in the fermenter (12), and an incinerator (17) into which is blown combustion exhaust gas of the biogas expelled from the combustor (15); the combustion exhaust gas of the biogas being blown into a primary combustion chamber (18) to which a stoker of the incinerator (17) is provided.
