To conduct readily the removal disposal of excavated matters brought together to its center by permitting the central part of a support with a plurality of cutters arranged to be slanted lower than its peripheral part, and rotation driving the cutter head.

The face plate of a cutter head 14 has an inverted conical shape, and accompanying the rotation and lowering of the cutter head 14, excavation is carried out in a V-shaped cross-section. The excavated matters come into the upper side of the face plate from the notch accompanying the rotation and lowering of the cutter head 14. The excavated matters moved into the upper side of the face plate not only move to the rotational center on the upper side of the face plate by its dead weight, but also move forcibly by the guide. Thus, the excavated matters can be gathered to the predetermined place positively and automatically with the result that the excavated matters can be disposed easily. After the excavated matters are collected to its center on the upper side of the face plate, they are discharged on the earth via the central part of the excavator 10 by means of a clamshell bucket 80.