A treatment tower of a carbon dioxide separation system includes a treatment container of a tower shape, having inner space which is virtually dividable into a regeneration treatment chamber, drying treatment chamber, and adsorption treatment chamber arranged in this order from the top to the bottom, by two hindrances which are upper and lower hindrances and hinder the downward movement of the adsorbent while maintaining the bedded (layered) flow of the adsorbent, a first passage member formed with ejection holes which eject a gas used in a treatment in each of the treatment chambers to a lower portion of each of the treatment chambers, and a second passage member formed with a gas discharge hole which discharges the gas having contacted the adsorbent from an upper portion of each of the treatment chambers. In the two treatment chambers on the lower side, gas discharge holes are formed below the hindrances.