A fluid treatment method that reduces the concentration of carbon dioxide included in a fluid-to-be-treated, the method comprising: a first step of reducing the concentration of water included in the fluid-to-be-treated by passing through a part of a rotating first rotor configured to mainly reduce water concentration to thereby obtain a first fluid, the first rotor having a cylindrical shape and being configured by silica gel with a honeycomb structure, the first rotor being configured to allow air to pass through in its axial direction; a second step of causing one part of the first fluid to pass through a carbon dioxide adsorption position, to thereby obtain a second fluid, the carbon dioxide adsorption position being a first part of a rotating second rotor (20, 220) configured to mainly reduce carbon dioxide concentration, the second rotor (20, 220) having a cylindrical shape and being configured by zeolite with a honeycomb structure, the second rotor (20, 220) being configured to allow air to pass through in its axial direction, the first part being capable of adsorbing both carbon dioxide and water and at least whose ability to adsorb carbon dioxide is temperature dependent, and through which the other part of the first fluid has passed; a regeneration step of causing a fourth fluid in which the concentration of water is lower than in the fluid-to-be-treated and whose temperature is higher than that of the fluid-to-be-treated to pass through a thermal regeneration position which is a second part of the rotating second rotor (20, 220) through which the one part of the first fluid has passed in the second step; a cooling step of causing the other part of the first fluid whose temperature is lower than that of the fourth fluid to pass through a cooling regeneration position, to thereby obtain a third fluid, the cooling regeneration position being a third part of the rotating second rotor (20, 220) through which the fourth fluid has passed in the regeneration step, the fourth fluid is a fluid obtained by heating the third fluid. a first step of reducing the concentration of water included in the fluid-to-be-treated by passing through a part of a rotating first rotor configured to mainly reduce water concentration to thereby obtain a first fluid, the first rotor having a cylindrical shape and being configured by silica gel with a honeycomb structure, the first rotor being configured to allow air to pass through in its axial direction; a second step of causing one part of the first fluid to pass through a carbon dioxide adsorption position, to thereby obtain a second fluid, the carbon dioxide adsorption position being a first part of a rotating second rotor (20, 220) configured to mainly reduce carbon dioxide concentration, the second rotor (20, 220) having a cylindrical shape and being configured by zeolite with a honeycomb structure, the second rotor (20, 220) being configured to allow air to pass through in its axial direction, the first part being capable of adsorbing both carbon dioxide and water and at least whose ability to adsorb carbon dioxide is temperature dependent, and through which the other part of the first fluid has passed; a regeneration step of causing a fourth fluid in which the concentration of water is lower than in the fluid-to-be-treated and whose temperature is higher than that of the fluid-to-be-treated to pass through a thermal regeneration position which is a second part of the rotating second rotor (20, 220) through which the one part of the first fluid has passed in the second step; a cooling step of causing the other part of the first fluid whose temperature is lower than that of the fourth fluid to pass through a cooling regeneration position, to thereby obtain a third fluid, the cooling regeneration position being a third part of the rotating second rotor (20, 220) through which the fourth fluid has passed in the regeneration step, the fourth fluid is a fluid obtained by heating the third fluid.