PURPOSE: To fix carbon dioxide using snow while conserving energy by a method wherein conc. separated carbon dioxide is mixed with snow to form a clathrate hydrate wherein a carbon dioxide molecule is incorporated in a water crystal and this clathrate hydrate is thrown away to the bottom of the sea in a very deep region.

CONSTITUTION: The CO2-containing exhaust gas discharged from a combustion furnace is guided to a pretreatment device to be lowered in its temp. and, after unburnt carbon is removed, only CO2 is conc. and separated. When this carbon dioxide is mixed with snow while held to about 10°C or lower, a clathrate hydrate wherein a carbon dioxide molecule is incorporated in snow or water crystals formed by the melting of snow is formed by chemical reaction at low temp. under pressure and sent to a clathrate separation tank 7 by a pump 6 and subjected to solid-liquid separation to be stored in a clathrate storage tank 8. Thereafter, the clathrate is enclosed in a container 9 and thrown to the bottom of the sea by a disposal ship 10 or a pressure feed pump. By this constitution, carbon dioxide is treated by a reduced amount of energy using snow present in the natural world skillfully.