PURPOSE: To make correction of misalignment of the shaft of a valve rod and varnishing of external thread simultaneously by synchronizing the difference in peripheral speed in rolling due to difference in diameter between the shaft of the valve rod and external thread with the difference in peripheral speed betweeen the thread roller and plain roller;

CONSTITUTION: A peripheral speed difference simultaneous rolling device 4 supports a pair of fixed axes 11, 11a and a pair of movable axes 12, 12a between a fixed bearing 13 and a movable bearing 13' in the upper part of a thread rolling board, and the fixed axes 11, 11a and movable axes 12, 12a are butted on the same axial line. Screw rollers 8, 8 for varnishing the external screw part 3 of the valve rod 1 and plain rollers 14, 14 for correcting misalignment holding and rotating the shaft 2 of the valve rod 1 are fitted at the butted ends. The difference in peripheral speed between the plain rollers 14, 14 and screw rollers 8, 8 adjusts the peripheral speed ration freely from relation of difference in diameter of driven gears 9b, 9b and driving gears 10b, 10b meshing therewith.