A method of regenerating an absorbent includes preparing a reactor having a gas inlet portion and a discharge portion, filling the reactor with a reforming catalyst and an absorbent for absorbing carbon dioxide, feeding the feedstock gas and the steam via the gas inlet portion to the reactor to allow a steam reforming reaction to take place, allowing the absorbent to absorb carbon dioxide generated with hydrogen at the steam reforming reaction, and releasing the carbon dioxide from the absorbent after the carbon dioxide absorption capacity of the absorbent has been degraded. In this method, the temperature in an inside of the reactor is set to 625° C. or more at the release of the carbon dioxide, and an inert gas is fed via the discharge portion to the reactor.