A carbon dioxide separation device comprising: an absorption tower into which an exhaust gas flows and configured to cause carbon dioxide, included in the exhaust gas, and an absorbent to react with each other; a first piping through which a CO 2 -rich-solution, obtained when the carbon dioxide and the absorbent reacted with each other, moves; a pressure reduction and phase separation unit arranged on the first piping and configured to depressurize at least a part of the CO 2 -rich-solution, and cause heat exchange between a lean solution and the depressurized CO 2 -rich-solution and separate the CO 2 -rich-solution into phases of a gas state and a liquid state; a stripping tower into which the CO 2 -rich-solution in the gas state and the CO 2 -rich-solution in the liquid state flow and configured to separate carbon dioxide from the CO 2 -rich-solution; a second piping configured to connect the stripping tower to the pressure reduction and phase separation unit so that the lean solution, obtained when the carbon dioxide is separated from the CO 2 -rich-solution, moves through the second piping; and a reheater configured to heat the stripping tower so that carbon dioxide is separated from the CO 2 -rich-solution, wherein the lean solution flows into the pressure reduction and phase separation unit, and the CO 2 -rich-solution undergoes the phase separation into the gas state and the liquid state due to heat of the lean solution, and then, flows into the stripping tower, wherein the CO 2 -rich-solution changed into the gas state is repressurized by a compressor or a fan and flows into the stripping tower, and wherein the CO 2 rich solution remaining in the liquid state is repressurized by a pump and flows into the stripping tower, characterized in that the CO 2 -rich-solution repressurized by the compressor or the fan flows into the lower part of the stripping tower, and the CO 2 -rich-solution repressurized by the pump flows into the center part of the stripping tower. an absorption tower into which an exhaust gas flows and configured to cause carbon dioxide, included in the exhaust gas, and an absorbent to react with each other; a first piping through which a CO 2 -rich-solution, obtained when the carbon dioxide and the absorbent reacted with each other, moves; a pressure reduction and phase separation unit arranged on the first piping and configured to depressurize at least a part of the CO 2 -rich-solution, and cause heat exchange between a lean solution and the depressurized CO 2 -rich-solution and separate the CO 2 -rich-solution into phases of a gas state and a liquid state; a stripping tower into which the CO 2 -rich-solution in the gas state and the CO 2 -rich-solution in the liquid state flow and configured to separate carbon dioxide from the CO 2 -rich-solution; a second piping configured to connect the stripping tower to the pressure reduction and phase separation unit so that the lean solution, obtained when the carbon dioxide is separated from the CO 2 -rich-solution, moves through the second piping; and a reheater configured to heat the stripping tower so that carbon dioxide is separated from the CO 2 -rich-solution, wherein the lean solution flows into the pressure reduction and phase separation unit, and the CO 2 -rich-solution undergoes the phase separation into the gas state and the liquid state due to heat of the lean solution, and then, flows into the stripping tower, wherein the CO 2 -rich-solution changed into the gas state is repressurized by a compressor or a fan and flows into the stripping tower, and wherein the CO 2 rich solution remaining in the liquid state is repressurized by a pump and flows into the stripping tower, characterized in that the CO 2 -rich-solution repressurized by the compressor or the fan flows into the lower part of the stripping tower, and the CO 2 -rich-solution repressurized by the pump flows into the center part of the stripping tower.