A process for producing slush nitrogen, comprising charging a low-temperature container with liquid nitrogen and arranging an ejector capable of drawing out liquid nitrogen by suction by spewing a refrigerant liquid or gas, such as low-temperature helium gas or liquid helium of pressure higher than in the space within the container, into the container so that the liquid nitrogen drawn out by suction by the refrigerant and spewed together with the refrigerant is refrigerated by the refrigerant, becomes particulate solid nitrogen and falls, while discharging the gas lying in the space within the container outside the container so as to constantly maintain the space at atmospheric pressure or higher. Further, there is provided a method of refrigerating a superconductive object including a substance exhibiting a superconductive state at temperatures close to the temperature of liquid nitrogen or close to the temperature at which the liquid nitrogen and the solid nitrogen coexist, characterized in that the object is immersed in slush nitrogen held in an adiabatic container so as to effect contact of the object with slush nitrogen and refrigeration thereof.