Abstract: A method of purifying an exhaust gas by way of an adsorption unit (adsorption columns 7a, 7b) including an adsorbent layer paced with precoated mesoporous active carbon capable of alternately switched operations of adsorption and desorption, wherein prior to the treatment by way of the adsorption unit, a concentration increase is effected by way of a pre-treatment unit (honeycomb rotor (11) or stationary honeycomb) including an adsorbent layer packed with precoated mesoporous active carbon for concentrating of any dilute volatile hydrocarbon contained in the exhaust gas. Consequently, there can be provided a method of purifying large amounts of exhaust gas with dilute volatile hydrocarbon concentration, in which without emission of carbon dioxide, any volatile hydrocarbon contained can be recovered with extreme easiness as a liquid. Further, there can be provided a purification method in which zero emission is attained with respect to volatile hydrocarbons.