Thermal storage medium using a hydrate and apparatus thereof, and method for producing the thermal storage medium

A thermal storage apparatus for using a hydrate thermal storage medium including: (a) a storage tank for storing a cooling medium liquid; (b) a refrigerating machine, connected with the storage tank via a pipe for cooling the cooling medium liquid, the cooling medium liquid circulating between the storage tank and the refrigerating machine; and (c) a thermal storage body immersed in the cooling medium liquid, wherein the thermal storage medium comprises a hermetically sealed container containing an aqueous solution which generates at least one hydrate selected from the group consisting of a primary hydrate and a secondary hydrate, wherein the primary hydrate has a smaller hydration number and a small heat capacity than the secondary hydrate, and wherein the secondary hydrate has a larger hydration number and a larger heat capacity than the primary hydrate.