force determined by the materials of the movable body 53 and others and a load to be supported vibration energy can be damped by utilizing absorption power which enables larger damping capacity next the following motion will be explained in the seismic isolation device 41 when the intensity of an external force added to the lower structure 42 or the magnitude of a vibration transmitted to the upper structure 43 is smaller than a predetermined value the air pump 60 is stopped to stop supplying air to the movable body 53 and when the intensity of an external force added to the lower structure 42 or the magnitude of a vibration transmitted to the upper structure 43 is more or equal to the predetermined value the air pump 60 is operated to feed air to the movable body 53 with this motion in a range where a vibration is relatively small until an external force corresponding to a frictional force determined by the materials of the movable body 53 and others and a load to be supported the upper structure 43 can immovably be maintained on the contrary when a vibration is large and the intensity of an external force becomes more or equal.