PURPOSE: To simplify underground construction work and to reduce the period of the construction work by providing the lowermost body which can be slid down, and utilizing the lowermost body to sequentially construct basements and beams.

CONSTITUTION: A continuous underground wall 12 is constructed and a plurality of underground posts 14 are constructed from the ground in an inside portion surrounded by the continuous underground wall 12. Next, drilling is carried out up to approximately the middle portion of a basement 10a to be constructed. The lowermost body 18 is downwardly slidably constructed on a plane 16 of drilling while being trimmed from the continuous underground wall 12 and the underground posts 14. The lowermost body 18 is temporarily secured to the continuous underground wall 12, and the first floor 20 and beams 22 are constructed and also drilling is carried out below the lowermost body 18 up to approximately the middle portion of the second basement. When the floor 20 and the beams 22 attain predetermined strength, the temporarily secured lowermost body 18 is released and slid down to the plane of drilling of the second basement and thereafter similar procedures are repeated to sequentially construct lower floors and beams.