Provided is an adsorbent adapted to adsorb carbon dioxide by increasing the pressure, and to carry out 10% or more adsorption and adsorption of the adsorbed carbon dioxide by lowering the pressure at atmospheric pressure or higher in a range of 100 to 900 kPa without vacuuming or the like. As a result of using amorphous aluminum silicate with a Si/Al ratio of 0.7 to 1.0 and having a peak in the vicinity of −78 ppm and −87 ppm in a 29Si solid NMR spectrum, adsorption and desorption of 10 wt % or more can be performed in a range of 100 to 900 kPa, and this can be used as a carbon dioxide adsorbent mainly in the pressure swing adsorption method.