Abstract: A rolling die is provided for forming a rod member with a ball portion. The rolling die includes a first die member and a second die member facing the first die member. Each of the first die member and the second die member has a process surface. The process surface has a start forming portion having a process tooth configured to bite the rod member and an arc surface portion proximate the process tooth, an intermediate forming portion having the process tooth and a curved surface proximate the process tooth, the curved surfaced being configured to press the rod member to form an arched shape, and a finish forming portion having the process tooth and a hemispheric groove configured to press the rod member into the arched shape to form the ball portion.