PURPOSE: To thrust an underground construction accurately, enable excavation to be conducted efficiently, and prevent the ground from collapsing by providing together a pipe support part on the front surface upper side of a fitting frame at the front end of an underground construction and a blade edge on the front surface lower side.

CONSTITUTION: A cutting edge is formed by providing integrally a pipe support part 19 on the front surface of a fitting frame 20 to be fitted in the front end opening of an underground construction 3 and a blade edge 18 on the front surface lower part. Then, a cutting edge 17 and underground construction 3 are placed at a sliding table 16 within a shaft, and the fitting frame 20 is fitted in the construction 3; subsequently, the rear end part of a pipe roof 13 being force-inserted previously into the support part 19 is fixed by a bolt. After that, while compressing the construction 3 by a jack 24 and thus being thrusted to the shaft 8 side, ground at both side walls is excavated by the blade edge 18; simultaneously, the pipe roof 13 is extruded at the shaft 8 side while leaving friction cut members 12 secured to a turn buckle 26 or the like.