PURPOSE: To form a square shape hole in a material to be cut only by rotating a main spindle while pushing a tip surface of a tip against a surface of the material to be cut by arranging a rotation conversion mechanism to move a cutter body and the material to be cut relatively around the axis so as to draw a square shape locus.

CONSTITUTION: A tip surface of a tip 13 installed on the tip of a tool rotation spindle 7 is pushed against a surface of a material 16 to be cut, and when a main spindle 1 is rotated, the rotation is transmitted to the tool rotation spindle 7 through a flexible coupling 15, and as a result, the material 16 to be cut is cut by a cutting edge 14 of the tip 13. On the other hand, since the tool rotation spindle 7 is made rotatable freely along a guide surface 3 by a support member 8, when it rotates in cutting, the tool rotation spindle 7 rotates around the axis, and moves along the guide surface 3 so that the locus becomes a square shape. As a result, the cutting edge 14 also moves while drawing a square shape locus, so that a square shape hole 17 is formed in the material 16 to be cut.