PURPOSE: To improve the workability of die width changing by arranging a separating means having a separating member wider than the recessed part to formed to notched part.

CONSTITUTION: A separating means S mounts a moving block S3 to the tip of piston S2 of the cylinder S1 vertical to a frame h1 of a moving means H. A separating pin S4 having wedge shape platy tip is mounted to the moving block S3 by a fastening screw S6 screwed to a screw hole S5 pierced in the moving block S3. A recessed part d4 is formed to the notched part between adjacent thick thickness split dies 5d. When the separating pin S4 is inserted into the recessed part d4, because the thickness g1 is larger than the width g2 of recessed part d4, the thick thickness dies 5d are separated each other. Thus, the thick thickness split dies are easily separated from a center die or other thick thickness split die.