PURPOSE: To increase strength against outside pressure by projecting a large number of columnar hard bodies to the outside earth side in an arch-shape while overlapping their parts to form a retaining wall by which an underground part forming space is surrounded.

CONSTITUTION: A large number of columnar hard bodies 1 are gradually overlapped and are projected to the outside earth 3 side in an arch-shape to from a retaining wall T. Reinforced cores 2 of wide flange shape steels are buried in boundary positions Z of adjacent arch sections to reinforce. Spans L1 and L2 of the arch sections are set to approximate 2-5m and are equalized to a curvature radius R of the arch sections. Then, after the retaining wall T is constructed, the inside thereof is excavated to ensure an underground part forming space 5, and a structural underground part 6 is constructed. Successively, after the completion of construction, a blank space 5' between the peripheral surface of the underground part 6 and the retaining wall T is buried. According to the constitution, outside pressure of the outside earth, etc., can be strengthened by the columnar-hard bodies group 1.