Provided are a method for splitting longitudinally an end part of a metal plate or a metal rod having a rectangular, polygonal, or elliptical shape, in which the length of incision in the split portion can be freely adjusted and smooth split face can be formed; a metal part manufactured by such method; and a method for bonding such metal part. The present invention is characterized by the process comprising the steps of securing a metal plate by pinching both sides thereof with a clamping device, or securing a metal rod by pinching at least two opposite-facing portions on the periphery thereof with a clamping device; splitting longitudinally by slitting or cleaving the metal plate, or the metal rod, by pressing a slitting punch or a cleaving punch against the face of one end of the metal plate, or the metal rod; and advancing the splitting further by repeating the same operation of pressing the same punch stated above against the cleft of the splitting; and is characterized further in that, in each time of the press-splitting operation, the position of the clamping device on at least one side is moved in advance of the next pressing by a stroke corresponding to the distance from one end of the metal plate, or the metal rod, to the distal end of a split-desired portion.