To provide an earthquake resistant structure for a ridge, which can be formed directly from outside the ridge, and ensures excellent earthquake resistance, and to provide a seismically retrofitting method.

In construction of a tiled roof, the ridge 12 is arranged along an edge line of a roof main body 11. Flat tiles 11A, 11B are laid side by side on the roof main body 11, while ridge tiles (loosely convex tiles 12A and ridge top tiles 12E) are piled up on the ridge 12. Then plastered wall sections 22 are each formed in a gap between the flat tiles 11A and the loosely convex tiles 12A, and bridging materials 13 are each mounted along the plastered wall section 22. Each bridging material 13 is formed by applying an elastic adhesive to wall surfaces of the flat tiles 11A, 11B, the plastered wall section 22, and the loosely convex tiles 12A, in a manner binding the same together in one body, and hardening the adhesive.