PURPOSE: To make construction possible in a narrow construction site where a large type crawler transporter can not change its course or a construction site having a narrow alley and a narrow turning of road which must be passed through.

CONSTITUTION: An elevating base 11 to elevate along a guide 10 is provided on a short leader 2 provided on a small type crawler which can travel and change its course even in a narrow area. A rod chuck 13 rotatively driven by a motor 9 is provided on the elevating base 11. An telescopic boring rod 14 whose upper end is attached to the rod chuck 13 by chucking is set along the leader 2. The boring rod 14 is composed of at least two short connected steel pipes which are different in diameter and telescopically fitted inside and outside. An excavating blade 15, an agitating blade 16 and a discharging hole for ground hardening material are provided on the circumference of the tip of the most outside connected steel pipe. A locking mechanism 21 which mutually stretches out the inner and outer connected steel pipes 14a, 14b and connectedly locks their ends is provided in the upper end part of the outside connected steel pipe.