PURPOSE: To prevent harmful torsional torque from acting on a workpiece by constituting a lathe driving one of the driving motors in each spindle to be rotated by predetermined torque and the other to be rotated by torque smaller than the above described predetermined torque performing predetermined machining of a workpiece.

CONSTITUTION: When a workpiece 23, held between spindles 2a, 3a, is machined, of the spindles 2a, 3a, the spindle 3a, connected to a spindle driving motor 6 with smaller torque, acts so as to rotate in such a manner as to perform the drag rotary action for the other spindle 2a. Consequently, the spindles 2a, 3a synchronously rotate in the rotary angular speed of the spindle 2a connected to a spindle driving motor 5 driven rotating by the predetermined torque, even when each spindle 2a, 3a provides its characteristic (inertia, acceleration and deceleration characteristic, etc.) not coinciding. Accordingly, harmful torsional torque can be effectively prevented from acting on the workpiece 23 held between the spindles 2a, 3a.