PURPOSE: To lessen the amount of industrial waste, use an excavating machine also for placing a solidifying material, shorten the construction term, and give homogeneity to a continuous underground wall constructed, by separating the fine grain soil from the excavated material generated at the excavation stage for the underground wall, using it as aggregate for solidifying material to serve in the muddy water in the hole being excavated,

CONSTITUTION: The excavated material is classified at the excavation stage, and the obtained fine grain soil is included in a muddy water 17 so that the specific gravity of the muddy water 17 becomes over 1.1. A partitioning member 25 is installed at the boundary of this muddy water 17 with a solidifying material 4 to be placed, and the fine grain soil contained in the surplus muddy water substituted with the solidifying material 4 placed is used as aggregate. The pressure feed amount of the solidifying material 4 is balanced with the volume of this placing, and the partitioning member 25 is pulled up, and the muddy water 17 is substituted with the solidifying material 4, and thus an underground wall is constructed. Thereby inside of the hole excavated serves as a storage for the fine soil used as aggregate of the solidifying material 4, so that the excavated material can be made use of even in a narrow site of construction and the amount of industrial waste be lessened.