PURPOSE: To provide a manufacturing method for a mandrel for a blind rivet, by which the head part being free from eccentricity and uneven thickness to an axis of a stem for constituting a mandrel main body.

CONSTITUTION: A metallic wire rod 20 having a conical or pyramidical cut end part 20a is inserted/held and fixed by a pair of split dies 11, 11, and by pressurizing an upsetting margin 26 of prescribed length containing the cut end part 20a protruded from the upper end face 14 of the split die by a punch 12, the head part is headed and formed. Also, as for the puch 12, a conical or pyramidical recessed part 18 matched to the cut end part 20a is provided on the lower end face 17 being parallel to the upper end faces 14, 14 of the split dies, the cut end part 20a of the metallic wire rod 20 inserted/held and fixed by the split dies 11 is fitted closely to the recessed part 18, and in a state that both sides in the axial direction of the upsetting margin 26 are constrained, the upsetting margin is pressurized by the punch 12, bulged in the radial direction which is not constrated, and in a flat flange part, the head part in which a conical or pyramidical projecting part is protruded is headed and formed.