To provide a reinforcing structure for soft ground allowing a structure constructed on the soft ground to withstand earthquakes and creep load, while avoiding unequal settlement of the structure placed thereon.

A plurality of high-strength cores 14 each having a specific gravity lighter than the weight per unit volume of the ground Q to be reinforced are arranged within a reinforced space 12 formed in the ground to be reinforced, while leaving required gaps between the cores. A hardenable fluid is packed into the entire gaps and hardened to form an integrally hardened foundation body 16 having a specific gravity lighter than the ground to be reinforced, to construct the reinforcing structure 10 for the soft ground. The appropriate gaps which communicate with one another while covering the overall interior of the reinforced space are left between the adjacent cores and the hardenable fluid is packed into the gaps to accomplish the reinforcing structure supported in a floating condition on the soft ground and allowing a structure to be placed and supported thereon, while insuring high compressive strength and appropriate rigidity and tenacity.