To provide a small-sized ground improvement machine capable of improving the ground to a deeper position without changing a grip position of a rotary shaft, preventing an impediment to conveyance by the length of a leader, lowering gravity, having excellent versatility and, at the same time, inclining the leader to both right and left sides.

A leader 11 of a soil improvement machine 10 is capable of being freely bent. Then, the leader 11 is mounted to a turnable leader bearing bracket 9 provided to the front end of a boom 5 of a working vehicle main body having the same constitution as that of a hydraulic shovel main body constituted of a crawler type traveling truck 2, a swing body 3 mounted on the traveling truck in a turnable manner and the boom 5 borne on the swing body 3 in a turnable manner in a state capable of being turned to both right and left through a leader mounting pin 9a, and a leader turnable cylinder 14 capable of turning the leader to both right and left is mounted to the leader bearing bracket 9 with the leader mounting pin 9a as the fulcrum.