To provide a flow-forming method, by which a workpiece is formed into a thin-walled product by preventing a breakage developed from the root of a formed part, tensile stress to the workpiece is reduced, and the service life of a forming tool is elongated.

In the flow-forming method, a workpiece 1, which is rotated, is plastically worked by pressing a forming ball 6, which is attached to a forming tool 5 and rollable in all directions, against the workpiece 1 and rolling the forming ball 6. Even in ironing work or drawing work, the tensile stress produced on the workpiece 1 is reduced since only the rolling resistance of the forming ball 6 is applied on the workpiece 1 in the same way as in the case of shrinkage-forming, so that the workpiece 1 is plastically worked into the thin-walled product while preventing the breakage of the workpiece 1. Further, the forming ball 6 is rollable in all directions so that abrasion is made uniform, and thus the service life of the forming tool 5 is elongated.