To install a diaphragm wall in the ground containing an obstacle, with it remained in the ground.

Side diaphragm wall prepared holes 51 and 52 deeper than a position of the obstacle, are formed on both sides of the obstacle 1. An diaphragm wall cutter 10 is moved in the horizontal direction from a state of being positioned in the side diaphragm wall prepared holes 51 and 52, and a lower diaphragm wall prepared hole 60 is formed by excavating first and second partial areas 71 and 72 being a lower side area of the obstacle 1. A upper diaphragm wall prepared hole 56 is formed by lowering the diaphragm wall cutter from the ground surface above the obstacle 1. A bond is injected into these prepared holes, and is mixed with an excavated soil substance, and a curing suspension is generated. This suspension is hardened, to form the diaphragm wall.