The invention relates to a method and to an apparatus for separating and utilizing carbon dioxide. According to the invention, carbon dioxide (3a, 3b) is separated from air (1a) being conducted to a building and/or from air (1c,1d) being circulated in the building to reduce the level of carbon dioxide in indoor air (1b) of the building (4), the carbon dioxide (3a, 3b) is recovered, and the carbon dioxide is conducted to a carbon dioxide treatment stage (5), where a chemical compound (6) is formed from the carbon dioxide. In addition, the invention relates to the use of the method.