To provide a screw turning method for machining screw grooves having different lead angles by turning in a short time, without using ordinary tools for preparation.

A composite machining lathe 1 controls movements of a support base 3, a slide table 8, a lift table 9, a headstock 10, a tailstock 11, and a replacing arm 7 through an NC device. While pushing a cutting tool 5 held by a tool rest 4 to a workpiece W rotated around a Z axis by the headstock 10 and the tailstock 11, the lathe can move the support base 3 in a Z-axis direction and turn the screw groove in the workpiece W by relatively moving the cutting tool 5 to the workpiece W. When turning the screw groove, the cutting tool 5 can be rotatably indexed around a tool spindle according to the lead angle of the screw groove.