PURPOSE: To reduce the cost by inserting a guide shaft supporting a wire saw into an underground wall pit, moving it in a circular arc shape while excavating sediment, bending the setting depth section of an underground continuous wall, and shortening the setting depth section.

CONSTITUTION: An underground wall pit 30 having a linear cross section is excavated tin the nearly vertical direction from the ground surface, then guide pits 31 deeper than the wall pit 30 are excavated nearly perpendicularly from both ends 30a, 30b. Two guide shafts 2 of an underground continuous wall pit excavation device 1 are inserted at both ends 30a, 30b. An endless wire saw 6 wound on the upper and lower rotary wheels 4, 5 of the shafts 2 is driven, the shafts 2 are thrust, and their tips are moved in a circular arc shape to excavate underground wall pit bend sections 32. A reinforcing material such as a wire mesh is erected in this underground wall pit 33, then concrete is placed. The tumbling of a self-supporting section and the sliding of a setting depth section by the weight of the soil on the bent setting depth section can be prevented, the short setting depth section can be self-supported, and the cost and construction period can be reduced.