PURPOSE: To inhibit the increase of specific resistance due to the hydration of hydraulic cement by incorporating the cement, a clay mineral, a polymer having high water absorbency, an electrically conductive substance and specified powder.

CONSTITUTION: Hydraulic cement is blended with 0.2-1.0 pt.wt. clay mineral such as bentonite based on 1.0 pt.wt. of the cement, 0.01-1.0 pt.wt. polymer having high water absorbency such as isobutylene-maleic anhydride polycondensation product, 0.01-0.1 pt.wt. electrically conductive substance such as NaCl and 1.0-3.0 pts.wt. limestone, silica or dolomite powder of ≤0.3mm grain size to obtain a ground resistance reducing agent. This reducing agent is sprinkled on the soil around a ground electrode and hardened with water in the soil.