A regeneration reactor of a CO2 capture system is disclosed. According to an embodiment of the present invention, in the CO2 capture system comprising a capture reactor selectively adsorbing CO2 by bringing a CO2-containing gas supplied from the outside into contact with a solid adsorbent, and a regeneration reactor separating the adsorbed CO2 from the solid adsorbent adsorbed with the CO2, the regeneration reactor includes a chamber having an inverted truncated cone shape being widened toward an upper part and narrowed toward a lower part, such that a pressure in the regeneration reactor is constantly maintained through the whole part and accordingly, a flow velocity in the chamber can be constantly maintained.