PURPOSE: To accomplish a safe and efficient addition of excavation rod members by moving a pile retaining apparatus adapted to grasp the pile upper end removably outward from the central position immediately below the power shaft of the drive section in such a manner as to be free to advance or retract.

CONSTITUTION: When a hollow pile P is driven throughout the length, the preceding auger screw S is separated from the power shaft 18 while removing the chuck 15 from the preceding hollow pile P after once the drive section is halted. As the drive section 4 and a retaining apparatus 7 are raised with a wire 5, a slide plate 13 is forced forward as shown by the long and two short dashes line with a hydraulic cylinder not illustrated. At this point, a new hollow pile is grasped with another crane 15 while a new auger screw S is brought down and inserted into the new hollow pile. In this case, the frontal overhanging of the guide cylinder 14 from the drive section 4 allows the new screw to be positioned right above the guide cylinder 4 without trouble.