To return an electronic device to its original position at the time of disappearing a seismic force by having a caster part composed of noncircular rotor whose radius is gradually increased.

When an seismic force is applied on a floor 7 and an electronic device 6 starts to move in the right side from the floor 7 side, a metal 3a and a noncircular wheel 1a are rotated by a horizontal rotation bearing 4 of a base isolating caster 5a by setting a contact point with the floor as a starting point and the isolation caster 5a is rotatingly moved in the right direction. Then, because the radius dimension of the noncircular wheel 1a is gradually increased according to the rotation angle, a shaft 2a moves in such a locus as climbing up an inclined face so as to release the seismic force, after that returns to its original position by the dead load of the electronic device 6, further moves in the left side, and swings in the left/right direction by drawing the locus as climbing the inclined face. After that, as the seismic force disappears, the moving amplitude is reduced so that the electronic device returns to its original position.