PURPOSE: To properly and quickly position the tip of a cutter and a mark line by arranging a rotary operating handle near to a boring device, with its handle shaft set upward.

CONSTITUTION: A feed screw 2 is rotated by a rotary operating handle 5, and a surface plate 3 is moved in the right or left direction to match the axis of the cutter 16 of a boring device 4 with the center point of a mark line. The rotary operating handle 5 is arranged near to the boring device 4 so that its handle shaft 5a is made parallel with the center axis of the cutter 16 of the boring device 4. The rotary operating handle 5 can be operated while the mark line of a work (a) is observed, and a tip can be set to a boring position while the line of sight is not detached from the mark line. The tip of the cutter 16 and the mark line can be properly and quickly positioned.