A CO2 removal device includes: a CO2 capturing material which captures H2O and CO2 in a gas; a reaction container which contains the CO2 capturing material; an H2O measuring unit for measuring the concentration of H2O in the gas; an H2O concentration adjustment device which adjusts the concentration of H2O on the basis of information obtained by the H2O measuring unit; a gas introduction path introducing the gas into the reaction container from the H2O concentration adjustment device and bringing the gas into contact with the CO2 capturing material; a first gas discharge path discharging the gas from the reaction container after the gas has been brought into contact with the CO2 capturing material; and a second gas discharge path discharging the gas that has been desorbed from the CO2 capturing material from the reaction container. The CO2 removal device allows for the reduction of energy consumption in removing CO2.