To provide a base isolation device capable of preventing the lubricant sealed in its inside from leaking to the outside and preventing the lubricant from being deteriorated with age due to its storage for a long time.

This base isolation device 1 installed between a lower side structural body 2 and an upper side structural body 4 of a building has a base member 3 installed in the lower side structural body 2, a building mounting member 5 positioned above the base member 3 and installed in the upper side structural body 4, and at least one ball 6 provided between a lower face of the building mounting member 5 and an upper face of the base member 3, abutted on at least one face selected from among upper and lower faces, and rolling freely. A protection ring 7 surrounding the ball 6 by leaving it or being abutted on it and having an upper end extended up to a proximity position where a clearance d for avoiding contact with the lower face of the building mounting member 5 or an upper face of the base member 3 is provided on the base member 3 or the building mounting member 5. The foaming solid lubricant 8 prepared by foaming and hardening a mixture containing a lubricating component, a resin component, hardener, and foaming agent is sealed in the protection ring 7.