PURPOSE: To extend cold insulation time sharply by providing two hydrate bags to contain a hydrate agent, and an endothermic bag to contain an endothermic agent, putting the hydrate agent contained in a first hydrate bag into the endothermic bag to cause endothermic reaction and hence lowering the temperature of the endothermic bag, and further lowering the temperature of the endothermic bag with the hydrate agent contained in a second hydrate bag.

CONSTITUTION: Hydrate bags 12A and 12B contain a hydrate agent 17 while an endothermic agent 18, which is mixed with the hydrate agent 17 to cause endothermic reaction, and a polymeric water absorption agent 19 are contained in an endothemric agent 13. A cap 15a of the first hydrate bag 12A and a cap 15c of the endothermic bag 13 are removed. Then, the hydrate agent 17 is thrown into the endothermic bag 13 so as to cause endothermic reaction and hence lower the temperature in the endothermic bag 13. The moisture separated is absorbed into the polymeric water absorption agent 19, turned into gel state, thereby upgrading slightly the continuity of the endothermic reaction. Then, the hydrate agent 17 contained in the second hydrate bag 12B is thrown into the endothermic bag 13 to cause the endothermic reaction again, thereby lowering the temperature in the endothermic bag 13 again. This construction makes it possible to obtain cold heat source indoors and outdoors in a hot season and use it for a long time.