PURPOSE: To decrease cost, to ensure sufficient strength, to easily ensure installation space, and to eliminate additional safety facility such as liquid preventing bank by filling liquid such as water in a space between an electrolyte tank and a civil engineering and construction structure tank.

CONSTITUTION: A tank 17 made of a plate such as resin and steel is put under the pressure of electrolyte 18 from the inside and the pressure of water 19 from the outside. The tank 17 needs only strength enough to resist to the difference of two direction pressure, and the strength is lowered. A water tank installed in the underground for stabilizing a building can be utilized as a concrete pit. Therefore, the installation space of the electrolyte tank is easily ensured. If the electrolyte 18 leaked from the tank 17, the leaked electrolyte is mixed with the water 19, and immediate leakage to the outside from the concrete pit can be prevented. Therefore, damage to the surroundings is avoidable.