A lead hole is formed in a base material of an injection hole member with a straight punch, and then, a taper hole is formed in the base material by widening the lead hole with a taper punch. An intersection line between a virtual plane perpendicular to a central axis of the lead hole and an inner peripheral surface of the lead hole is elliptic in shape, whose major axis is directed along an intersection line between a virtual plane, which includes the central axis of the lead hole and a thickness direction axis of the base material, and the virtual plane perpendicular to the central axis of the lead hole. An intersection line between a virtual plane perpendicular to a central axis of the taper punch and an outer peripheral surface of the taper punch is round in shape.