<p>A method of finishing a groove (Da) extending in a Y-direction of a work (D) with an offset tool (T) having such a shape (L3) of the cross section that is offset by a predetermined offset amount in a contracting direction relative to the finished shape (L1) of the groove and rotating around a rotating axis parallel with a Z-axis. Each time a cut-in step in which the offset tool (T) is relatively moved by a predetermined distance around the initial position along the circumference of a virtual circle (C) with a radius equal to the offset amount in an X-Z plane is performed, a cutting step in which the groove (Da) is cut over the entire length while the offset tool (T) is relatively moved in the Y-direction is repeatedly performed. Since the load exerted on the offset tool (T) can be lightened compared to a forming tool for cutting the wide area of the groove (Da) of the work (D) at a time, the durability of the offset tool (T) can be increased and the finishing precision of a machined surface can be increased.</p>
