To provide a method that effectively uses cold heat of LNG. ! A system has a step of transforming carbonic acid gas into liquefied carbonic acid with the use of cold of liquefied natural gas, a step of transferring the resultant liquefied carbonic acid, a step of transforming the transferred liquefied carbonic acid into carbonic acid gas and a step of transferring the resultant carbonic acid gas. ! (C)2003,JPO