PURPOSE: To improve a performance of product, by a method wherein a commercially available product such as an electrical resistor or the like which is usually applied in a predetermined range of temperature is cooled to a cryogenic temperature, and, after this cooled state is held only for a predetermined time, its temperature is increased up to a predetermined range of temperature, a residual stress in the product is reduced or substance of it is stabilized. CONSTITUTION: A blower 15 is fixed to a bottom part of a power head 1 so as to feed cooling nitrogen gas flowing around some fins 13 of a heat exchanger 4 to a Dewar chamber 2 within a housing 3. At this time, the power head 1 is lifted up and after a product, i.e., load to be treated is stored in the chamber 2, the power head 1 is returned back to its original state and fastened to it. Then, a solenoid valve 18 is opened to feed liquid nitrogen from a supplying pipe 19 to a pan 21 so as to cool the pan 21 and some fins 13. In addition, the same very low temperature gaseous nitrogen vapor as liquid nitrogen is flowed from each of openings 45, 49 into the chamber 2 so as to cool the load. Meanwhile electrical power is supplied from a high temperature limit switch 25 to a heating element 14, thereby applying heat to the load or the like under utilization of convection flow generated by the blower 15.
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