PURPOSE: To accurately and continuously pierce numerous holes on an annular angle stock by providing a turning device movable in the pressing direction of a V-type driving roller and the diameter direction of a supporting plate and a punch set movable in the diameter direction of the supporting plate.

CONSTITUTION: The supporting plate 9 corresponding to an annular angle stock 25 is fitted to each pressing plate 7 by descending a center shaft 4 and retreating an annular angle stock turning device 16 and a punch set 23 as well. Thereafter, the annular angle stock 25 is outer-fitted to the supporting plate 9 and placed on 1st, 2nd rollers 10, 11 to ascend the center shaft. The supporting plate 9 together with pressing plate 7 are then slid in a radial direction to fix the outer peripheral face by press-welding it to the inner peripheral face of the angle stock 25. The turning device 16 and punch set 23 are then moved to the specified position and after the press-contact of the V-type driving roller 20 of the turning device 16 to the upper face of the horizontal piece of the angle stock 25 and the outer side face of a vertical piece, it is rotated and the angle stock 25 is turned intermittently on each specific pitch on a receiving roller 11 to execute piercing by the punch set.