To utilize the waste oil containing the chlorine compound substance effectively, microwave-induced nonequilibrium plasma of the glow charge type was applied to spray combustion of the used electrical insulation oil containing the chlorine compound substance. The spray combustion experiment was conducted in a quartz reaction tube with microwave-induced nonequilibrium plasma. Many O and H radicals are generated by the electron impact dissociation reactions O-2 + e -> 20 + e and CmHn + e -> CmHn-1 + H + e (hydrocarbon CmHn is produced by vaporization of insulation oil) under nonequilibrium plasma, and many OH radicals are produced by the O + CmHn and O + H reactions. Because O and OH radicals play an important role in the combustion reaction and work as a combustion reaction promoter, the ignition and combustion of insulation oil are enhanced under nonequilibrium plasma. As a result, the flammability limit of combustion of insulation oil is expanded and the heat flow rate of the exhaust gas increases under nonequilibrium plasma, because the exhaust gas volume and flow rate of combustible gases such as H-2 and CO are increased.