Abstract: A machining apparatus simultaneously machining at least two portions of one workpiece is disclosed. The machining apparatus includes a worktable unit for rotatably driving workpiece, at least two tool heads each of which supports a tool and moves forward to or away from the workpiece, at least two gauging units measuring a diameter of each portion, and control unit controlling motion of each wheel head individually. The control unit controls motions of the wheel heads in according to signals provided from the gauging units, wherein controls all of tool heads to execute a finish grinding process, controls one tool head corresponding to one portion whose diameter became a required value to back off, and controls all of tool heads to execute a spark-out process after diameters of all of the portions became each required value. Therefore, it can prevent that accuracy of one portion machined by one tool head is deteriorated by effect of machining by another wheel head.