PURPOSE: To prevent the oxidation of an edible oil for a long period, and to preserve the oil for a long time safely without deteriorating the taste and flavor, by forming an electrical field between a pair of electrodes, and putting the edible oil in the electrical field.

CONSTITUTION: When radicals are generated in the edible oil stored in the case 1, the radicals are attracted to the electrode 2 or to the surface of the case 1 by the electrical field in the oil, and the radical density is locally increased. In the region having high radical density, the radicals are bonded with each other forming a stable compound which does not cause a chain reaction. The oxidation of the oil can be terminated by this process. Since the oil has high viscosity and the migration of the radical is slow, the radical cannot exactly follow the AC electrical field, and consequently, it is effective to use a DC or DC- containing electric source.