To allow a pressed excavation process and a forced pile drive by applying the constitution that a bracket for mounting an auger drive motor and a pile forcing device is caused to slide via the expansion and contraction of a hydraulic cylinder.

Upon the expansion of a hydraulic cylinder 7, an end leader 4b as well expands by the same length. Concurrently, an upper sprocket 10 ascends by the same length, and an auger drive motor 5 or a bracket 6 ascends over a distance two times as long as the expansion of the cylinder 7, due to the travel of an upper chain 15 wound around the sprocket 10. Then, when an earth auger is mounted on the motor 5 or a pile forcing device is mounted on the bracket 6 for holding a pile and the cylinder 7 is made to contract, the motor 5 or the bracket 6 descends over a distance two times, as long as the dcontraction of the cylinder 7. At the same time, a lower sprocket 13 descends by a distance equivalent to the contraction of the cylinder 7 and a downward pressing force acts on the motor 5 or the bracrket 6 via a lower chain 14, thereby keeping a sufficient biting amount.