A system for transferring, positioning and machining a workpiece includes a transfer device for transferring the workpiece to a prescribed position, a positioning device disposed in the prescribed position for positioning the workpiece, a machine tool for machining the workpiece, and a delivery robot disposed in the prescribed position for delivering the workpiece to the machine tool. The positioning device is used to position workpieces successively. Therefore, it is not necessary to provide positioning devices which would otherwise be associated with respective workpieces. The positioning device includes a positioning pin which is displaceable toward and away from a workpiece. Since the positioning pin is not held against the workpiece at all times, the positioning pin is prevented from being damaged or broken by physical interference with surface irregularities of the workpiece.