PURPOSE: To reduce the period of construction, and to prevent the collapse and slackening of circumferential ground, and also to prevent the damage of sound parts due to vibration at the time of disassembling work.

CONSTITUTION: An angle adjustment hydraulic jack 4 is operated in the extension/ contraction directions, so that a frame 11 is oscillated with a pivotally supporting link 12 as a center for adjusting the angle of the frame 11. Then, a ball valve 13 (not shown) for preventing the inflow of stones and sand and water is opened, and a rod-feeding hydraulic jack 5 is operated for moving an extension type rod 7 forward. And the foremost end thereof is penetrated into the ground at the front through the opening 15 (not shown) that has been provided to a cutter-supporting shaft 3 and through the opening 16 (not shown) that has been provided to a turning member 1 having a cutter 2, and a conical cone 6 having a water-jet nozzle 19 (not shown) is positioned obliquely in front of an obstacle. Then, a water-jet producing pump 10 is started, and pressurized water is jetted obliquely rearwards as a water jet against an obstacle 20 (not shown) via a flexible hose 9, a swivel joint 8, the hollow extension type rod 7, the pressure water passage inside the conical cone 6, and a nozzle 19 (not shown) for cutting the obstacle 20. At that time, most of the jetted pressure water is collected inside the cutter chamber 2 through the opening 16 of the turning member 1.