To produce a steel cord capable of improving tire slalom durability in reinforcing the belt layer of a pneumatic radial tire by periodically imparting kinks mutually different in shape, pitch and amplitude to each element wire.

The steel cords 6 each made of one element wire (having a diameter d=0.30-0.50 mm) are buried as reinforcing cords in a belt layer to form a pneumatic radial tire. A repeating unit R comprising several kinds of kinks mutually different in at least one of shape, pitch and amplitude, in which a kink pitch P and amplitude H of wave shape or the like vary respectively in the range of [(5-50)d] and [(0.1-5)d].