Disclosed is an apparatus for processing an exhaust gas containing an alkaline substance, the exhaust gas being emitted when activating a carbon material with an alkaline substance. The apparatus includes a humidified-gas preparing device for preparing a humidified gas, which exhibits a dew point of 25° C. or more; a gas mixing device for mixing the humidified gas with the exhaust gas at a temperature equal to or greater than the dewpoint of the humidified gas, thereby generating a hydroxide of metallic alkali; and a trapping device for trapping the generated hydroxide out of the mixture gas of the humidified gas and the exhaust gas.