To prevent float between a plate body and a filler when a timbering is removed after construction by providing an elastic member in a position abutting with the plate body in a repairing or reinforcing work for surrounding an existing structure by the plate body, and injecting a filler between the both.

When a square steel pipe 14 is fixed by a fixture 15, and a fluidized mortar 12 is then filled in the clearance between a steel plate 13 and an existing bridge beam 11, the steel plate 13 receives an internal pressure and expands outward. Since a foamed sponge 20 is compressed between the steel plate 13 and the square steel pipe 14 so as to be deformable, the steel plate 13 can be expanded to some degree toward the outside. Namely, the steel plate 13 is expanded up to the range regulated by the surface of the foamed sponge 20 when the foamed sponge 20 stuck to the inner surface of the square steel pipe 14 reaches the compression limit. Thus, even if the timbering of the square steel pipe 14 or the fixture 15 is removed after a fluidized mortar 12 is hardened, the steel plate 13 is in the expanded state with the inward force still acting thereon, and integrated with the fluidized mortar 12.