Abstract: The invention provides a novel carbon dioxide adsorbent that can capture carbon dioxide and the like, the carbon dioxide adsorbent being a carbon dioxide adsorbent including a metal-organic framework, the metal-organic framework can capture and desorb carbon dioxide, an isolated voids are formed inside the metal-organic framework by the metal-organic framework's three-dimensional structure, the isolated voids are the space that can capture carbon dioxide and does not have a channel through which carbon dioxide can pass in an ordinary state, and although the three-dimensional structure of the framework changes during the process where carbon dioxide is captured within isolated voids and the process where carbon dioxide is released from isolated voids, the three-dimensional structure of the metal-organic framework when carbon dioxide is captured within the isolated voids is the same as when carbon dioxide is not captured within the isolated voids.