To substitute stable substances in contact reaction with chlorine remaining in generated gas.

In a gas combustor 7, a combustion burner 3 is provided for rendering generated gas such as introduced water vapor or dry distilled gas harmless after complete combustion treatment under the conditions of 800°C or higher and two seconds or longer. A plurality of gas stirring members 74 are provided for stirring combustion gas to create sufficient combustion effects. In the gas combustor 7, medical agent is sprayed from an A-point, as shown in Fig., for producing harmless chloride in contact reaction with chlorine as a structural element for dioxines. However, for the sprayed medical agent, harmless substances (chloride) are substituted in contact reaction with the decomposed chlorine because the gas combustor 7 has a high temperature of 800°C.