To secure horizontal base isolation performance while simplifying a structure, and further maintain vertical base isolation performance even if a pneumatic spring is horizontally sheared and deformed.

The base isolation device 1 includes a plurality of pneumatic springs 2 disposed horizontally between an upper structure and a lower structure. Each of the pneumatic springs 2 includes a film-like cylindrical member 3 extending vertically with both upper and lower ends being closed, an outer fitting member 5 fitted onto the film-like cylindrical member 3, and an upper attachment member 6 and a lower attachment member 7 disposed respectively on both upper and lower ends of the film-like cylindrical member 3, the upper attachment member 6 being attached the upper structure, and the lower attachment member 7 being attached to the upper structure. The respective outer fitting members 5 of the pneumatic springs 2 adjoining horizontally are mutually connected through a connecting member 9.