PURPOSE: To provide possibility of boring two or more metal sheets continuously by furnishing a pluaity of splash exhaust grooves at the periphery of a cylindrical member for boring, by recessing a cutting edge piece at the bottom corner of cutter body formed between each pair of adjoining exhaust grooves, and by forming the cutting edge piece from a specific outer and inner edges.

CONSTITUTION: Splash exhaust grooves 4 are cut at the periphery of the lower circumferential wall 1b of a cylindrical member 1 for boring at a constant spacing to form a cutter body 5 between each pair of adjoining exhaust grooves 4. The bottom surface of each cutter body 5 is protruded down in the rotational direction, and a cutting edge piece 6 is recessed at the bottom corner as in contact with the front edge of the cutter body 5. Each cutting edge piece 6 is forme from an inner 6a and outer 6b edges alternately, wherein the inner edge 6a shall be a downward facing angle edge having an edge width corresponding to approx. half the thickness of cutting edge piece 6 situated nearer the inside of bottom surface of the cutting edge piece 6, while the outer edge 6b a downward facing slant edge having an edge width corresponding to approx. half the thickness of the cutting edge piece 6 situated nearer the outside of the bottom surface of the cutting edge piece 6. The bottom surface of this cutting edge piece 6 is cut so that the inner 6a and outer 6b edges both protrude downward.