To provide a deterioration prevention system for a lubricant having superior oxidation preventing effects at the time of storage and use of the lubricant without using large-sized facilities.

The deterioration prevention system comprises (1) a step of making inactive gas generate from an inactive gas generating device, (2) a step of supplying generated inactive gas into a lubricant storage device, and (3) a step of controlling the concentration of inactive gas in the storage device at a range of 90 to 99.9%.