PURPOSE: To improve the machining accuracy or surface roughness and to suppress the variance of the finished dimension in the hobbing by shifting the hobbing shaft to machine the finishing part after machining the rough machining part

CONSTITUTION: In the No.1 cycle the work is rough machined in the rough machining part 31 and the finish machining of the same cycle is done in the finish machining part 21. Next, the rough machining of the No.2 cycle is done at the position with its generating center D shifted by the predetermined amount D from that of the No.1 cycle, and the finish machining is done at the position with the generating center E same as that of the No.1 cycle. By shifting the generating center in the subsequent cycle by the predetermined amount when machining the machining accuracy or the surface roughness can be improved and the variance of the finished dimension can be suppressed.