PURPOSE: To prevent sinking of an existing structure, by a method wherein a new structure is built below an existing structure, temporarily supported, and a filling substance is implanted into filling bodies between the two structures to expand and cure it, and the own weight of the existing structure is transferred to the new structure.

CONSTITUTION: A foundation 3 of an existing structure 1 is coupled to a temporary support beam 4, and through operation of a jack placed between the temporary support beam 4 and support piles 2, 2b so that the temporary support beam 4 is jacked up, the own weight W of the structure 1 is transferred to the support piles 2a and 2b to sink and stabilize the support piles 2a, 2b. A temporary support material 6 is then inserted between the tempoary support beam 4 and the support piles 2a, 2b, the jack is removed, and a new structure 8 is constructed right below the existing structure 1. Cement paste 18 is placed in a cloth bag 10 of a filling body 9 located between the foundation 3 and the new building structure 8, mortar 19 is deposited in a cloth bag 11 to expand and cure the filling body 9, and this causes occurring of sinking by δ3 of the structure 8 by serving the own weight W of the structure 1 as a reaction force.