Abstract: An end surface machining apparatus is provided, wherein an end surface of a first workpiece is machined with a second workpiece being inserted into the first workpiece. First and second in-process gauges are engageable at their feelers with the end surface of the first workpiece and a reference end surface of the second workpiece during machining, respectively. A feed device is provided to move a work support toward the tool in the axial direction of the workpieces. A control device, controllably connected to the feed device, is responsive to output signals from both the in-process gauges, so that the end surface of the first workpiece is machined to have a predetermined size difference relative to the reference end surface of the second workpiece.