To provide cutoff method and device for repairing the periphery of an underwater part of a bridge pier, by which at the time of remodeling the underwater part of the bridge pier in the aerial condition, a considerable amount of cost and time will not be needed for cutoff work, and sure cutoff can be done.

Segments 2 are constructed like a cylinder on a sponge seal 3 laid like a circumference in such a manner as to surround the outer periphery of the underwater part of a bridge pier 1 to form an outer enclosure, and a P-type seal 4 is arrangd on the bottom of the outer periphery of the sponge seal 3. Further, cylindrical steel plates 5 are fitted at designated spaces to the outer periphery of the outer enclosure. After that, a water proof sheet 6 is arranged between the outer enclosure 10 and the steel plate 5, and clay 7 is filled thereon to perform cutoff.