PURPOSE: To enable groove machining with high efficiency by synchronizing material feeding speed with tool shaft rotation, continuously feeding a material into a machining point at a rate of one groove pitch to one tool rotation and machining grooves at an equal pitch.

CONSTITUTION: By synchronizing the feeding speed of a material W with a tool shaft rotation, the material W is continuously fed into a machining point at the rate of one groove pitch to one rotation of the tool 2 to carry out groove machining at an equal pitch. By this structure, in machining the workpiece W, since the workpiece W is fed while being interfered with the tool 2 at a speed synchronized with the rotation of the tool 2, continuous equal pitch grooves can be machined. Hence, grooves which are arranged at a certain pitch can be machined on the bar type material W with high efficiency.