To provide a seismic butt isolation structure that can maintain the soundness of a butt by preventing the application of an excessive shearing force or bending moment to the butt at an earthquake while maintaining the stability of a joint between the butt and a foundation slab.

A flange plate 3 having a diameter larger than a pile diameter and having a plurality of holes 4 in a peripheral portion is fixed to the butt 1. A stud 14 is loosely inserted in each hole 4, and the upper end of each stud 14 is secured in the foundation slab 12. The foundation slab 12 forms a void 13 allowing the horizontal deformation of the stud 14 between the securing portion and the flange plate 3.