Machine tool workpiece (P) conveying device according to the present invention includes: a first screening jig 10 capable of contact with the horizontal end portion of the workpiece (P); First selection means of transportation (20); First selection sensor (30) and; And the possible second screening jig 40 contacts the upper end of the workpiece (P); Second selection means of transportation (50) and; Second selection sensor (60) and; Of the first and second selected sensor (30, 60) when one or more are on (ON) of the first and second said work on the basis of whether the on / off of the selected sensor (30, 60) (P) If the length or to find out the thickness information that is called a response after identifying the type of work piece (P) corresponding to a part program, and the first and second selected sensor (30, 60) both off (oFF) thereof, the alarm signal PMC (70) for generating and; It characterized in that it comprises a CNC unit (80) for machining a workpiece (P) according to a processing program called from the PMC (70). Workpiece, screening, piston, machine tools, transfer