PURPOSE: To enhance water stopping performance by abutting both side parts of a seal plate on the opposed surfaces of a pair of concrete joints respectively, and by tightening and fixing the seal plate by means of bolts via pressing plates.

CONSTITUTION: Concrete is placed in the stepped-down part 6 of a styrene-foam forming frame to form a pair of concrete joints 2 having opposed corrugated longitudinal concrete surfaces 2a, and then the forming frame is heated and melted away. After both side parts of a seal plate have been abutted on the opposed longitudinal concrete surfaces 2a, the bolts 12 projected from the longitudinal concrete surfaces 2a are inserted in the long holes of pressing plates 11, and the respective pressing plates 11 are superposed on both the end parts of the seal plate. Then, nuts are screwed on the bolts 12, and both the side parts of the seal plate are tightened and fixed to the respective concrete surfaces 2a via the pressing plates 11. Further, a sealing material 13 is filled in the groove formed by the pressing plates 1, longitudinal concrete surfaces 2a, and the seal plate.