PURPOSE: To form a large diameter pile hole without applying an excessive load to an auger motor while using conventional small diameter excavating rods and screws by rotating a main shaft and a sub-shaft by a main driving motor, and rotating a base body by a sub-driving motors.

CONSTITUTION: A circular base body 2 is inserted and arranged in a housing 1 constituting an adapter, and this is made freely rotatable by sub-driving motors 5A and 5B, and a main shaft assembly 3 and sub-main shaft assemblies 4A, 4B and 4C passing penetratingly vertically through the center are installed, and a female type joint 41 is installed on the lower end, and is connected to excavating rods A. A male type joint 31 is arranged on the end of the main shaft assembly 3, and is connected to an auger motor M. Next, the auger motor M is driven through the male type joint 31, and when a main shaft is rotated, the female type joint 41 rotates, and the excavating rods also start to rotate, and the ground is agitated and crushed by agitating blades A1 of the respective excavating rods A, and a larger diameter hole is excavated.