To significantly improve productivity by obviating the necessity of paying attention to breakage of a mold, and extremely prolonging the life of a mold.

An angular hole 6 is provided in a sliding piece 3, and an relief hole 7 is penetrated to a sliding surface 3a in the same direction as the angular hole 6 via a space 6 from the angular inlet 6a of the angular hole 6. A female screw 7a is made in the vicinity of the sliding surface 3a of the relief hole 7. An angular pin guide bush 8 having a guide hole 8a is slidably provided internally in the part except the female screw part 7a in the relief hole 7. The sliding range of the angular pin guide bush 8 is decided in its lower limit by a position adjustable stopper 9 screw-engaged in the female screw 7a of the relief hole 7. Then, a belleville spring 10 is interposed between the stopper 9 and the angular pin guide bush 8.