A method and an apparatus for concentrating/purifying a chlorine gas are disclosed in which a pressure swing adsorption method for alternately repeating an adsorbing operation and a desorbing operation employing one or more adsorption towers packed with an adsorbent for adsorbing the chlorine gas are used to obtain a high-purity concentrated/purified chlorine gas and an exhaust gas containing virtually no chlorine gas is obtained from the chlorine gas containing impurities by terminating the adsorption operation when the rate of temperature rise near the outlet end of an adsorption tower due to adsorption of chlorine therein rises above a predetermined amount.