There are provided a carbon dioxide storage apparatus and a carbon dioxide storage method which, through direct injection of carbon dioxide into an underground brine aquifer, can store carbon dioxide efficiently in the brine aquifer. A filter formed of, for example, grindstone is provided at a tip portion of an injection well. A pumping apparatus pumps carbon dioxide stored in a carbon dioxide tank. The pumping apparatus feeds carbon dioxide from the carbon dioxide tank into the injection well by means of a pump. In the pumping apparatus, carbon dioxide is held within a predetermined pressure range and a predetermined temperature range. Carbon dioxide is fed through the injection well, and is injected into a brine aquifer. Carbon dioxide injected into the brine aquifer assumes the form of microbubbles.