To efficiently excavate even a soft rock-bed.

Four drilling means 35 are rotatably fitted to a ringlike drilling edge 2 rotated at a front end part of a head excavating pipe. The drilling means 35 is provided with an rotational axis R with the tip side inclined onto the excavating direction side as well as on the inner diameter side of the ring- like drilling edge 2, and a plural rows of drilling tips are fitted to the outer peripheral surface, along the direction of the rotational axis R.