To provide a ball stud of a ball joint, capable of improving productivity and a yield rate of material.

A first intermediary formed body 54, providing an approximately columnar portion 51 corresponding to a shaft, which has an approximately spherical portion 62, corresponding to a head connected at an end in succession and an approximately columnar portion 53 corresponding to a screw thread in the same axis at an another end, is forged from approximately columnar material 45. A second intermediary formed body 56, having a seated face 26, in which the portion 51 corresponding to the shaft, is fitted on an installed portion by forging in a precise and easy manner, and also padding a flanged connecting portion 28, which becomes the standard of a relative position with the installed portion, is formed. By means of fitting a connecting face 27 of the connecting portion 28 with the side faces of a fixed fie and movable die, a neck portion 22, having a diameter smaller than a shaft portion 23, is rolled between the portion 52 corresponding to the head and the connecting portion 28. A projected portion 29 for sealing is rolled by padding in a flanged state through material flow generated, while the neck portion 22 is performed rolling. The portion 52 corresponding to the head is finished, a male screw thread is formed on the portion 53, corresponding to the screw thread, and the ball stud 6 is formed accordingly.