PURPOSE: To improve the dimensional accuracy by forming the clearance groove which extends in the axial direction on the inner face part of each guide corresponding to the place becoming narrow between the cross like ball grooves of a forming item and by forming the projecting part engaging to the clearance groove on the punch as well.

CONSTITUTION: A cylindrical billet 11 is inputted between each punch 4, 9 of the upper die 2 and lower die 3. The punch 4, 9 are approached after placing the upper die 2 and lower die 3 at the prescribed interval. The billet 11 is bulged into a segmental die 5 by the pressure of each punch 4, 9. In this case, the billet 11a bulging on the clearance groove 16 is pushed into the place 18 where the space between ball grooves 7 becomes narrow. With this device the shortage in push-in is eliminated and the dimensional accuracy of a product can be improved.