To provide a base isolation structure for a building sufficiently exhibiting the base isolation performance even if a building main body is light- weight.

This base isolation structure 4 for a building is provided with a foundation side member 41 provided on a building foundation and a building side member 42 provided in the building main body 3 and supported by the foundation side member 41, the foundation member 41 and the building side member 42 have recessed curve faces 413, 421 respectively, and a spherical body 43 is slidably interposed between the recessed curve faces 413, 421. The recessed curve face 421 in the building side member 42 and the foundation side member 41 are slidably constituted so that the base isolation structure 4 insulating the building foundation from the building main body 3 can be constituted and the setting of the curvature of the recessed curve face 421 allows to ensure the desired base isolation performance without influence of the weight of the building main body 3.