PURPOSE: To ensure the construction accuracy by performing operations by unmanned machines.

CONSTITUTION: Guide rail members 1 are vertically driven from the ground surface to the bearing ground 2 surface, and a foundation part loaded with preceding excavating tools 5 and pipings, and an underground structural part of a floor directly above the foundation part, are constructed on the ground surface. Rollers 9 for rolling the guide members 1 are installed to the side wall of the structural part, and jet water is jetted from the tip excavating tools 5 of the foundation part to sink the underground structural part to a specified depth. Excavating operation is performed by excavating robots loaded with flexible hoses 7, by utilizing water of the excavated parts. Thereafter, these processes are repeated.