To make working efficiency high and improve the positional precision of boring at the time when the boring is performed continuously by repeatedly performing the boring while an auger is moved along a guide ruler set along a guide planned position.

The lower part of a leader 3 is fixed on a guide ruler set along a planned boring position, and boring is performed while an auger 2 is guided on the guide ruler 6. Furthermore these operations are repeated while the auger 2 and the leader 3 are moved at an adjacent position along the guide ruler 6 to perform the boring high in positional precision. In the case, movement for the adjacent position along the guide ruler 6 of the auger 2 and the leader 3 is performed to turn a boom and perform extension and contraction and ups and downs of the boom. Furthermore the movement of a crane vehicle is unneeded for the movement of the auger 2 and the leader 3 to enable the movement only by turning, extension and contraction and ups and downs of the boom. Thereby the position precision of the continuously forming boring is improved, and working efficiency can be improved even for work or the like in the center of the narrow city of a working area.