PURPOSE: To improve workability and transportability by dividing a leader vertically movably supporting a screw auger, connecting them into a spigot type, and providing an expandable hydraulic jack in a lower leader.

CONSTITUTION: A leader 4 suspended by the boom B of a crane and supporting a screw auger main body 2 along a guide pipe 7 is vertically divided, and the divided leaders are expandably connected into a spigot type. The lower leader 6 is provided with a driving device for expanding/shrinking actions constituted of a hydraulic jack. When the work is conducted at a site having a limit in height such as under a bridge or an electric wire, the leader 4 is shortened, a screw 3 is fitted to it, and an excavation is made by the auger 2. The hydraulic jack can be connected to an external hydraulic source via a hose, or another air cylinder can be used. The leader 4 can be divided into three or more. Workability and transportability can be improved.