PURPOSE: To prevent pollution, e.g., caused by the use of bentonite liquid, etc., in excavation by a method wherein after excavation by auger screw, residual soil in pit is recorvered and then a cement mortar, etc., is injected for foot protection.

CONSTITUTION: An excavator is installed, and then a steel pipe 2 and an auger screw having an auger head on its top are turned in mutually reverse directions by drivers 4 and 5 for excavation. Then, the auger screw 3 alone is drawn out leaving the steel pipe 2 underground and a bucket 6 is attached to the auger screw 3 to recover soil in the bottom of the excavated pit. Then, the auger screw 3 is pulled up while injecting a cement paste into the pipe 10 so as to fill the cement paste in the bottom of the pit. Then, a concrete pile is inserted into the steel pipe 2 and filling material piled up on the ground around the steel pipe 2 is filled into the aperture around the pile by means of the screw 1 synchronously with the pulling-up of the steel pipe 2.