PURPOSE: To reduce the cost of construction work by settling and fixing a prefabricated concrete basement body having inside walls whose outer faces are subjected to a water-proofing treatment, fixed at an adequate interval, with side walls, a bottom wall and ceiling wall, in a hole excavated under the ground.

CONSTITUTION: Inside walls 2 whose outer faces are subjected to a water-proofing treatment are fixed at an adequate interval (a) to the inside of a concrete basement body 1 having side walls 1A with cutting edges 1D on its lower ends, a bottom wall 1B and a ceiling wall 1C. A pit 3 for drain pump and a latticed drain groove 4 are formed in the bottom wall 1B, and the side walls 1A are set on a place where a basement is to be constructed. The ground below the basement body 1 is excavated, the excavated soil is discharged from the inside of the side walls 1A, and the basement body 1 is sunk with its own weight. Leveling concrete 7 is placed to the bottom of the inside space of the side walls 1A to fix the bottom wall 1B. The construction period can thus be shortened and the construction cost of the basement can also be reduced.