PURPOSE: To improve the efficiency of work, by a method wherein after a ring frame structure is organized with a shaft core of a supporting rod fixed in ground and the tip of the structure is thrust into ground by a jack via a pressure receiver, ground is excavated by a bit fitted on the structure.

CONSTITUTION: After a supporting rod 10 is fixed in the ground, a ring frame structure 12 is organized with a central shaft of the rod 10 portion exposed on the ground. Then, a pressure receiver 16 is held by the rod 10, and the lower face of the pressure receiver 16 is pressed by a jack 14, and the lower end section 13 of the structure 12 is thrust in ground. Then, a rotary shearing device 15 is worked for excavation and a retaining frame 7 is organized, and excavated earth is discharged by using a bucket 4. And after the pressure of the jack 14 is released and the pressure receiver 16 is held downward, eafth is excavated to a specified depth in the same way.