To prevent initial excess cooling, by mixing hollow balls made of plastic and coated by a thin magnetic film, adhering an aluminum foil on one inner face of a bag filled bey a cold insulator, and conducting weak current to move the plastic balls to the aluminum foil side in a cold insulator liquefying process.

Hollow plastic balls 2 mixed with thin magnetic film coated hollow plastic balls and a cold insulator 3 are housed in a bag 1. An aluminum foil 4 is adhered on one face of the bag 1. When the cold insulator bag 1 is freezed in a refrigerator, plastic balls 2 are collected at the upper face by the difference of specific gravity and freezed and solidified. When the freezed and solidified face is used by applying to a body, convection is generated by body heat to move the plastic balls with low specific gravity gradually upward causing to obtain uniform cooling effect. Further, the plastic balls are moved by energizing to the aluminum foil 4 causing to obtain further uniform cooling effect.