A crimping die includes a first die for constraining the wire crimping portion by a concave die surface shaped in conformity with the wire crimping portion, and a second die including a convex die surface paired with the concave die surface. A width of a recess on the concave die surface and that of a projection on the convex die surface are equal to an outer diameter of the wire crimping portion. The wire crimping portion is pressed by the concave die surface of the first die and the convex die surface of the second die, whereby the wire crimping portion and the wire inserted into the cylindrical interior of the wire crimping portion are crimped and fixed.