PURPOSE: To prepare stabilizing liquid of uniform concentration in mass production quickly by disposing a submerged pump with a suction hole and a plurality of discharge outlets in a agitation water tank connecting a sludge transfer pipe to one of said discharge outlets and connecting bentonite suction pump to the base end of another discharge outlet.

CONSTITUTION: A valve 26 installed in a sludge transfer pipe 24 is closed and water is sucked from a suction hole 16 into an impeller casing 13 by operating a submerged pump 12, passed through discharge outlets 17a, 17b and nozzles 18a, 18b and jetted out into an agitation tank 10. At that time, the pressure in the discharge outlets 17a, 17b becomes negative, and powdery bentonite 22 in a bentonite accommodating bag 21 is passed through suction pipes 19c, 19a and 19b, jetted out into respective discharge outlets 17a, 17b and also jetted out from jetting nozzles 18a, 18b into a water agitation tank 10. After that, when a valve 26 is opened, stabilized liquid is fed from a discharge outlet 17c to an excavated hole or the like through a sludge transfer pipe 24.