PURPOSE: To produce effective thrust successfully applicable to works to be carried out in rugged stratum by providing a percussion driving device at the rear end of a ground-hardening agent injection rod, and by giving percussion to the rod when the rod is inserted into the ground.

CONSTITUTION: A ground-hardening agent injection rod 5 is inserted into a ground W that is to be hardened, and by injecting the hardening agent, by operation of the rod 5, from a ejection nozzle 52 at the tip of the rod 5, a stratum with the hardening agent injected therein is prepared. At executing a work by this method, a percussion driving device 44 is installed at the rear end of the rod 5 and percussion is applied thereby for thrusting the rod 5. Impulsive force by the percussion is dispersed by turning effect of the rod and is uniformly extended into the ground, absorbing distortion and compaction by earth pressure, and the thrust produced thereby effectively works. Vibration at the injection is further enhanced by the percussion, shaking the whole area of the injection hole and allowing lubricating oil to infiltrate throughout the hole, and obstacles existing ahead of the rod 5 can be easily crushed thereby.