PURPOSE: To construct a basement in a short time by a method in which precast concrete bottom slabs are laid on the bottom of a hole, a precast box part to make up a basement is set on the bottom slabs, and the surrounding of the box part is embedded with soil.

CONSTITUTION: A hole H is formed by excavation of the ground's surface on site, precast concrete bottom slabs 1 of a two split structure are set on the bottom of the hole H. Precast concrete box parts 6 (6d and 6b) of a two split structure are set on the bottom slabs 1 and these component parts are connected. Afterwards, the surrounding of the box parts 6 is back-filled with soil and a structure, e.g., a housing, etc., is constructed on the box parts 6. Since the structural parts of the basement are made of precast concrete, the period of the construction can be shortened and the quality of the basement can be stabilized.