PURPOSE: To control an artificial freezing area without affecting a peripheral structure by controlling a frozen area.

CONSTITUTION: A freezing pipe 9 is set near a sheathing wall 3, and a heater 11 is set between the sheathing wall 3 and the freezing pipe 9. A coolant is poured into the freezing pipe 9, and the ground including a leakage part 7 is frozen to generate a frozen area. The length of an inner pipe 15 is regulated on the basis of the position of the leakage part 7, and hot water is circulated to the heater 11. The freezing of the ground between the sheathing wall 3 above the leakage part 7 and a heating pipe 13 is arrested, and the ground within a narrow range including the leakage part 7 is frozen.