A method for machining the outer circumference of the cross section of any of the end of a metal rod or a metal pipe, the drawn end of a metal rod or a metal pipe, and a hub hole forming part on a metal pipe by splitting method using a slitting punch to form at least any one of a deep groove, a deep recess, and a flange on the periphery thereof, wherein the tip of the slitting punch has a sharp cutting edge of the same or partly same outline as the cross section of the end of any of the metal rod or the metal pipe, the drawn end of the metal rod or the metal pipe, and the hub hole forming part on the metal pipe, wherein the diameter of the slitting punch is smaller than the outer diameter of the cross section of the splitting object; and the method includes the processing step of abutting the slitting punch on a position on the periphery of the cross section of the end of any of the metal rod or the metal pipe, the drawn end of the metal rod or the metal pipe, and the hub hole forming part on the metal pipe to form a cleft; and the method characterised by: advancing further the splitting in the longitudinal direction of the metal rod or the metal pipe by repeating the press-splitting operation by the slitting punch at the cleft for further or repeatedly one or two or more times; wherein, when machining the outer circumference of the cross section of any one of the end of the metal pipe, the drawn end thereof, and the hub hole forming part thereon, the depth of the cleft created in the metal by the press-splitting each time of the press-splitting operation is adjusted in advance by disposing one end of one side of the set of clamping dies (5, 6), which pinch the inside and the outside of the metal pipe at opposite positions in a state of contacting with whole circumferential surfaces of both sides, at the same position as the fore-end of a split-desired portion from the edge of one end face of the metal pipe, and by disposing one side of the other side of the set of clamping dies (5, 6) at the same position as the fore-end of a split-desired portion from the edge of one end face of the metal pipe, or at the same position as the edge of the end face of the metal pipe so as to support the metal pipe, and when machining the outer circumference of the cross section of any one of the metal rod end and the drawn end of the metal rod, the depth of the cleft created in the metal by the press-splitting each time of the press-splitting operation is adjusted in advance by disposing one end of the clamping die, which pinches the outside of the metal rod in a state of contacting with whole circumferential surface of the outside thereof, at the same position as the fore-end of a split-desired portion from the edge of the one end face of the metal rod. advancing further the splitting in the longitudinal direction of the metal rod or the metal pipe by repeating the press-splitting operation by the slitting punch at the cleft for further or repeatedly one or two or more times; wherein, when machining the outer circumference of the cross section of any one of the end of the metal pipe, the drawn end thereof, and the hub hole forming part thereon, the depth of the cleft created in the metal by the press-splitting each time of the press-splitting operation is adjusted in advance by disposing one end of one side of the set of clamping dies (5, 6), which pinch the inside and the outside of the metal pipe at opposite positions in a state of contacting with whole circumferential surfaces of both sides, at the same position as the fore-end of a split-desired portion from the edge of one end face of the metal pipe, and by disposing one side of the other side of the set of clamping dies (5, 6) at the same position as the fore-end of a split-desired portion from the edge of one end face of the metal pipe, or at the same position as the edge of the end face of the metal pipe so as to support the metal pipe, and when machining the outer circumference of the cross section of any one of the metal rod end and the drawn end of the metal rod, the depth of the cleft created in the metal by the press-splitting each time of the press-splitting operation is adjusted in advance by disposing one end of the clamping die, which pinches the outside of the metal rod in a state of contacting with whole circumferential surface of the outside thereof, at the same position as the fore-end of a split-desired portion from the edge of the one end face of the metal rod.