PURPOSE: To independently operate an LNG system and a generator system by cooling LNG with antifreezing fluid, cooling carbon dioxide with the fluid, then cooling the working fluid with the carbon dioxide, and storing the antifreezing fluid and the carbon dioxide in a reservoir. CONSTITUTION: A carbon dioxide reservoir 17 is evacuated to evaporate part of liquid carbon dioxide in the reservoir to obtain carbon dioxide gas, and to solidify other part. The evaporated carbon dioxide is condensed by heat exchange with antifreezing fluid to be supplied from an antifreezing fluid reservoir 9 for storing antifreezing fluid of lower temperature than the carbon dioxide gas, and the antifreezing fluid is heated. The condensed carbon dioxide is returned to the reservoir 17 to generate solid carbon dioxide in the reservoir. The heated antifreezing fluid is cooled through heat exchange with liquefied natural gas(LNG), the LNG is vaporized, the cooled antifreezing fluid is returned to the reservoir 9 to obtain antifreezing fluid of lower temperature than the gas carbon dioxide. Thus, an electric power generation is performed while the utility of cold is held high.