PURPOSE: To prevent occurrence of front cracks on the way of cutting a plate body involving wooden fibers by engraving a plurality of grooves at optional intervals on the back of the tip of cutting edge.

CONSTITUTION: Grooves 13 having a curved surface of a specified sectional shape are engraved on the back 11 of the tip of cutter edge of a round cutter 10 having a certain inclination angle on the periphery with its cutting edge formed to an annular shape, thus the annular cutting edge 16 is formed. A rotary cylindrical body 19 is arranged to oppose to the cutting edge 16 and to partially overlappingly contact with this cutting edge 16, so that the side 20 contacts partially and overlapping with the back 11 the tip of the cutting edge. A plate body 22 to be fed by a conveyer 24 is cut off to provide the satisfactory cut surface without producing front cracks between the cylindrical body 19 and the cutting edge 16.