The hole expansion processing method, and a molding tool having a linear projection formed so as to protrude outward from the surface of the enlarged diameter portion and the enlarged diameter portion whose diameter increases toward the rear end from the front end side , preparation process and to prepare the workpiece which the lower hole is formed; for some of the peripheral edge of the prepared hole of the workpiece, the linear projection of the tooling is in contact two or more points having; the sequential spread the prepared hole of the tooling by pushing the prepared hole as the hole expansion step of forming a stretch flange.