VERTICAL HOLE DRILLING BIT

PROBLEM TO BE SOLVED: To drill a vertical hole with a desired diameter according to the kind of a vertical hole and also always transport each bit in the assembled state by removably assembling a small-diameter bit at the tip, a medium- diameter bit in the middle and a largediameter bit at the base end in such a manner as to be substantially like an inverted cone and connecting the same one another. SOLUTION: A vertical hole drilling bit M installed at the lower end of a rotary auger (m) comprises a small-diameter bit A, a mediumdiameter bit B and a large-diameter bit C, wherein each bit is formed by a cutter suspended on the lower surface of a three-way radial rotary b de, a connecting shaft having a substantially rectangular section, and a fitting hole. The small-diameter bit A, the medium-diameter bit B in the middle, and the largediameter bit C at the base end are respectively removably assembled in such a manner as to be substantially like an inverted cone to be connected to one another. In the case of erecting a power mast, drilling is performed by the whole formed like an inverted cone, and in the case of erecting a mast for telephone works, drilling is performed by the combination of the medium-diameter bit B and the small-diameter bit A without the large-diameter bit C.