PURPOSE: To construct a circular vertical shaft of great depth wherein the thickness of a landslide protection wall and the depth of embedment are reduced, workability is improved, and economy is increased.

CONSTITUTION: A vertical shaft is excavated inwater inside a cylindrical landslide protection wall 2 constructed inside the ground 1 and a plurality of flexible tubes 7 are cylindrically arranged inside the vertical shaft. A liquid-setting material 10 is pressed into the tubes 7 and a reinforcing ring 13 is constructed inside the landslide protection wall 2. Bottom concrete 15 is placed inwater and then water is drained from the inside of the vertical shaft.