PURPOSE: To preserve and transport an ion source while inexpensively and easily preventing oxidation of an ion material in a preserving method for the ion source.

CONSTITUTION: In a preserving device composed of a cap 1 and a vessel 2, an ion source is preserved in the vessel in a condition where the inside of the vessel 2 is filled with liquid. In this way, since an ion material is prevented from being exposed to air, the ion source is preserved and transported while preventing oxidation of the ion material. Therefore, the ion source can be preserved and transported while inexpensively and easily preventing the oxidation of the ion material.