SCREW ROTOR MACHINING METHOD, MACHINING DEVICE AND MACHINING TOOL, AND METHOD OF MANUFACTURING SCREW COMPRESSOR

In a method of machining a screw rotor (1) to form a screw tooth-groove (2) by simultaneously controlling about a plurality of rotation axes for use in rotating a workpiece and turning a tool, the method includes a process step of drilling into a desired depth, a process step of performing rough machining of side-faces (41) of a screw tooth-groove (2), a process step of performing finish machining of side-faces (41) of a screw tooth-groove (2), and a process step of performing finish machining of a bottom-face (43) of a screw tooth-groove (2); and, at the finish machining process step on the bottom-face (43) of the screw tooth-groove (2), it is so arranged as to use an end mill (28) being provided with a cutting edge having, in its size, the quantity of axial depth of cut or more along a side-face of the end mill (28), which also has its front-end shape corresponding to a bottom-face of a screw tooth-groove (2) and has an outer periphery geometry less than or equal to a tool diameter capable of being inserted down to a groove bottom of the screw tooth-groove (2) in a maximum tooth-groove depth position.