A machining system 1 comprises a lathe 10 having end portion supporting mechanisms 13, 15 for supporting an elongated workpiece W horizontally, center rests 21 for supporting the middle portion of the workpiece W, an adjustment mechanism for adjusting the supported position of the workpiece W by adjusting the height positions of the center rests 21, a tool rest 20, and a control device 25, and a non-contact measuring device 30 for measuring the deflection amount of the workpiece W at portions thereof supported by the center rests 21 when the workpiece W is rotated. The control device 25 is configured to adjust the height positions of the center rests 21 by controlling the adjustment mechanism on the basis of the measured deflection amount, so that the height positions of both end portions of the workpiece W being rotated and the middle portion thereof become the same.