The present invention provides a carbon dioxide separation device comprising: an absorption tower for causing reaction between carbon dioxide and an absorbent; a first piping through which co2-rich-solution moves; a pressure reduction and phase separation unit arranged on the first piping, for separating the phase of the co2-rich-solution into gas and liquid; a stripping tower, into which the co2-rich-solution in gas and liquid states flows, and which separates carbon dioxide from the co2-rich-solution; a second piping for connecting the stripping tower and the pressure reduction and phase separation unit such that a lean solution, which results from removal of the carbon dioxide, moves; and a reheater for providing the stripping tower with heat such that carbon dioxide is separated from the co2-rich-solution, wherein the lean solution flows into the pressure reduction and phase separation unit, and the co2-rich-solution undergoes phase separation into gas and liquid, by means of heat of the lean solution, an
