the shift base 16 to move thereon the second support 14b of the support block 14 has a tapped hole 14c in which to receive therein a ball screw 19 which is coupled to a rotary shaft of a pulse motor 18 a work holder 20 is divided into two segments to form mount elements 20a and 20b which are secured to the supports 14a and 14b respectively a spacer 21 is fixed at the mount element 20a end and extends to the mount element 20b end a slot 21a is formed at the mount element 20b end of the spacer 21 said slot 21a to receive a screw not shown attached to the mount element 20b a lock lever not shown is engaged with the screw with this arrangement the lock lever is loosened to adjust the distance between the mount elements 20a and 20b the mount elements 20a and 20b carry thereon lower blades 22a and 22b mounted thereto a pair of shift brackets 23 includes braces 23a and 23b which are slidably fitted over the loader spindles 15a and 15b respectively a loader drive shaft 24 is disposed to pass through the braces 23a and 23 b to slidably move the latter a pair of levers 25a and 25b are coupled to the loader drive shaft 24 at the opposite ends thereof said levers are adapted to be driven by cylinders not shown panels 26a and 26b are firmly mounted atop the braces 23a and 23b atop panels 26a and 26b are setting devices 27a and 27b and work clamps 28a and 28b also.