PURPOSE: To effectively dehydrate even in a refrigerator oil of high dissolving properties in water by introducing dry gas with its dew point temperature is lower than the specified temperature in a tank when the refrigerator oil is jetted into a space in a vacuum exhausted tank.

CONSTITUTION: Refrigerator oil 2 (example: polyglycolic refrigerator oil) is stored in a bottom section of a tank 1, and the refrigerator oil 2 is jetted into a space 4 in the tank 1 by a circulating pump 3. Also, when the refrigerator oil 2 is jetted into the space 4 in the tank 1 vacuum exhausted by a vacuum pump 6, dry gas 8 (example: air) with its dew point temperature of -48°C or lower is introduced into the tank 1. That is, the moisture contained the refrigerator is adsorbed by the dry gas 8 and exhausted therefrom to reduce effectively the moisture contained in the refrigerator oil of high dissolving properties in water.