Abstract: An earth boring apparatus for driving a boring tool, the tool having a head for penetrating the earth and a longitudinally extending rotary drive shaft (15) for advancing the head. A carriage (18) is mounted to support frame (10) for advancing movement so as to advance and retract the drive shaft (15) and head. A drive shaft extension can be fitted between the carriage (18) and the drive shaft (15) thereby extending the effective length of the drive shaft (15). The apparatus includes a shaft engaging member (40) associated with the frame (10) and selectively operative to engage the shaft (15) having the head thereon and to inhibit rotation thereof thereby enabling the carriage (18) to be retracted and the drive shaft extension to be fitted between the carriage (18) and the shaft (15).