To provide a method for seismic strengthening construction for a caisson quay adaptable even to the behavior of a rubble mound in an earthquake of a level 2 without stopping the operation of the quay.

The installation of guide pipes 7b, the pre-boring of a foundation rubble mound to a predetermined position, and the intrusion of a cylindrical structure 8b are performed at the top of a caisson quay. The cylindrical structure 8b forms a continuous beam having extension parts projecting from the bottom and top of a caisson wall body 1. When the quay is used, the construction is interrupted between the constructions, and a cap 17 for temporary recovery is fitted to the top of the cylindrical structure 8b and an apron 5 is released.