without difficulty by using an auger crane and adjustable excavating unit application_number US 99051406 A description hereafter a preferred embodiment of the present invention will be described fig1 is an exploded perspective view of an adjustable excavating unit for an auger crane according to the present invention fig2 is a perspective view of an assembled adjustable excavating unit for an auger crane according to the present invention fig3 is a cross sectional view of an excavating unit for forming an excavation hole for a small sized under bracing according to the present invention and fig4 is a cross sectional view of an excavating unit showing an extended state for forming an excavation hole for a large sized under bracing according to the present invention an extendable excavating unit for an auger crane for mechanized construction of earth wire under bracing for utility pole work is mounted to the excavating end portion of an auger shaft 10 having a spiral auger scoop blade 11 formed thereon and has protruded excavation teeth 12 disposed opposite to each other the extendable excavating unit comprises an excavating unit 20 mounted to the excavating end portion of the auger shaft 10 the excavating unit 20 includes supporting units 24 protruding from opposite sides covering units 27 which can slide.