PURPOSE: To obtain an anchor bolt having a high accuracy with a high efficiency by grasping a thick shaft part and a collar part so that they cannot be expanded, pushing and hitting the end part of a thin shaft part, and forming by pressure an inverted conical body, in an anchor bolt material which has formed the collar part, the thin shaft part and the thick shaft part.

CONSTITUTION: A anchor bolt material 50' having a collar part 50d, a thin shaft 50a and a thick shaft part 50e is formed from a metallic base material rod, pushed into a die 9, and the thick shaft part 50e and the collar part 50d are supported in an immobile state. The thin shaft part 50a is inserted into a conical split die chuck 12 incorporated in a punch 4, and the thin shaft part 50a is grasped and held by each split die piece 12a. Subsequently, a projecting circle part 16a of a punch projecting die body 16 is fitted into an opening 12b of the rear end of the chuck 12, and the opening part is closed up tightly. The end face of the thin shaft part 50a is hit strongly by the projecting circle part 16a, and simultaneously, the center part of the end face is hit strongly and concentrically by a center pine 18, too. Therefore, the tip of the thin shaft part 50a is overhung in a conical space 20 and an inverted conical body is formed. In this regard, a screw part is formed by a thread rolling die 21 in the thick shaft part 50e, and a prescribed another bolt 50" is obtained.