The purpose of the present invention to develop an adsorbent having exceptional adsorption of carbon dioxide, and to provide an apparatus for concentration of carbon dioxide in the air through the use thereof. Provided is a carbon dioxide concentrating apparatus comprising a concentrating apparatus of pressure swing system using particle-shaped ferrierite as adsorbent, the particle-shaped ferrierite having particle diameter of 0.5 through 5 mm, the particle-shaped ferrierite being subjected to treatment by means of an aqueous solution of hydroxide in concentration of 1.5 through 5 mol/L at the room temperature to have pores in diameter of 0.01 through 1 μm and pore volume of 0.1 mL/g or more, the concentrating apparatus having two adsorption towers of carbon dioxide and a reservoir tank.
