PURPOSE: To precisely and easily form a fine deep hole or an open hole by, moving a drill forward by way of constantly keeping the head end of a guide cylindrical body and a material adjacent to each other or at a position where they make contact with each other.

CONSTITUTION: The rear end of a drill shank 12 of a deep hole drilling tool is installed on a drill chuck and is rotated. At this time, not only a drill 11 but also a guide cylindrical body 13 and a cylindrical body 15 rotate together. It is favourable that the head end of the drill 11 is projected about 2mm to about 2.5mm from the head end of the guide cylindrical body 13. Thereafter, when the head end of the drill 11 is made contact with a material of about 6mm thick to be drilled, the drill 11 rectilinearly advances into the material. Interlocked with this rectilinear advancement, the guide cylindrical body 13 moves backward against force of a coil spring. In this way, the drill 11 rectilinearly advances into the material, and a through hole of 0.5mm in diameter which is extremely high in precision of verticality is formed.