GROUND IMPROVING DEVICE

PROBLEM TO BE SOLVED: To provide a ground improving device which admits use of a long stretching excavation shaft and whose center of gravity can be set low stably even when the works are applied to a large area using a plurality of excavation shafts. SOLUTION: A ground improving device concerned 1 includes a plurality of excavation shafts 10 having an outer shaft 11 and inner shaft 12 which are rotated in the opposite directions where a working head 70 is connected at the tip. The arrangement comprises an excavation shaft driving device 20 installed under a leader and equipped with a prime mover 21 and a transmission mechanism 22 for transmitting the power of the prime mover 21 to the outer shafts 11 of the excavation shafts 10, a rotation synchronizing device 40 installed between the outer shafts 11 for synchronizing the rotations of the outer shafts 11, and an excavation shaft elevating/sinking device 50 which is arranged over the device 20 as capable of elevating and sinking along the leader, to which the tops of the outer shaft 11 and inner shaft 12 of the excavation shafts 10 are mounted, and which is equipped with a reversely transmitting mechanism 51 for elevating and sinking the excavation shafts 10 and transmitting the powers of the outer shafts 11 to the inner shafts 12.