To install easily even if position relatively disposed along horizontal direction of installation holes in respective upper structure and lower structure is different from design.

In an aseismatic base isolation device 1 of which an elastic body 16 is interposed between a pair of two-pieces end plates 14, 15 individually fixed to the upper 11 and the lower structures 12 by a fixing bolt 13, in the end plates 14, 15, it is formed on outer peripheral portions 14a, 15a protruded from the elastic body 16 to outside of radial direction with an accommodation hole 21 in which an adapter plate 20 is rotatably fitted and is formed on the adapter plate 20 with an elongated hole 22 through which the fixing bolt 13 is inserted.