To turn a recessed groove easily by pressing a cutting tool against a machined face of a workpiece and vibrating the cutting tool in the direction of pressing while transferring the cutting tool in the orthogonal direction to the direction of pressing.

A first travel table 6 and a second travel table 11 are moved to bring a tip of a cutting tool 5 into contact with a machining start point of a workpiece 9. After that, while moving the first travel table 6 at predetermined speed, a drive signal generator 10 is controlled so that an output pulse having shorter cycle than rotation cycle of a main spindle 4 is obtained, and the cutting tool 5 is vibrated in X direction at cycle of one-integral number of the rotation cycle of the main spindle 4, namely, the workpiece 9 for cutting. Consequently, a spiral recessed groove having the width equal to cutting width of the cutting tool 5 is formed on a machined face of the workpiece 9.