PURPOSE: To install a building unit precisely by protruding two or more anchor bolt upper parts at the oversurface of a riser part of a precast concrete foundation, and coupling together the lower parts of the anchor bolts within the riser part.

CONSTITUTION: Main rods 27 and ribs are arranged in the riser part 21 and base 22 of a precast concrete foundation. Two or more anchor bolts 23 are arranged at the riser part 21, and the lower parts 23 of the anchor bolts 23 are coupled together within the riser part 21. At executing the works, a house unit is installed in such a way as put over the foundation 2, and the anchor bolts 23 are threaded in through holes provided at the undersurface of each column or floor beam of the building unit, followed by driving-in of nuts, and thus the unit is secured onto the foundation 2.