PURPOSE: To obtain lubricant oil that can prevent a cracked gas formed by exposure to radiation from being diffused, and therefore, can be employed in parts that may be exposed to radiation by dispersing a specific substance in perfluoroether oil.

CONSTITUTION: In 100 parts by weight perfluoroether oil (e.g. BARRIERTA-J100 F manufactured by NOK Klueber Co., Ltd.), about 10-8 to 100 parts by weight, preferably 10-2 to 3 parts by weight, finely divided metal oxide having an average particle size of preferably 1,000 μm or less, still preferably 3 μm or less (e.g. MgO, CaO, or Li2O) is dispersed to obtain lubricant oil.