To lengthen a time span up to repair by making a bridge a long life by solving the problem that rainwater, muddy water or the like leaks from a loose gap to accelerate aging of a concrete structure of a floor slab and an iron member of a main girder or a concrete member and the problem that since salt is spread, in particular, in a district supposing road surface freezing and waterproofness is imperfect, salt damage of a girder and a pier of a bridge occurs.

The flexible absorbent structure allows a plate-like interlocking body GX coupled to one floor slab concrete to cover the upper part of a loose gap GG, arranges so as to come into face contact with the other floor slab concrete high step part, arranges to shift an expansion means in a gap GY between the end of the plate-like interlocking body G and the notch rise part of the other floor slab concrete, absorbs the expansion of a joint part on the other floor slab concrete, and does not leak in the loose gap even when the expansion means damages.