To easily and surely agitate soil and a solidifying material by preventing cohesive soil from sticking to the periphery of an agitating blade as a mass, even if the object ground is the cohesive soil.

This multi-shaft auger suspends a plurality of excavating shafts 4 from a driving device 3 suspended and supported by a leader mast 2 of heavy machinery 1. Horizontal or almost horizontal horizontal plate blades 8 composed of radial three blades are properly arranged at vertical intervals as agitating blades and shearing blades on the respective excavating shafts 4. The horizontal or almost horizontal horizontal plate blades 8 of the mutual adjacent excavating shafts 4 are superimposed at a tip part in a vertical position. In the excavating shafts 4, an excavating head 6 is arranged on the tip, a screw blade 7 is arranged over the head, and the horizontal or almost horizontal horizontal plate blades 8 are arranged further over the screw blades 7.