To provide a soil improvement apparatus which is good in soil improving efficiency and can make its excavation shaft penetrate the ground at an arbitrary angle.

A link device 211 formed of a 4-node rotation link mechanism is arranged at the tip of a boom 205 of a base machine 201, a hydraulic motor 213 is installed to the link device 211, and the excavating shaft 1 having an excavating blade 11 is connected to a rotating shaft of the motor. The link device 211 is driven by a hydraulic cylinder 210 attached to a front-side boom 204. Thus, by operating the hydraulic cylinder 210, the link device 211 is dislocated, and the axial J direction of the excavator shaft 1 can be adjusted.