A high-strength, ultra-fine wire having an excellent workability in stranding, comprising a steel comprised of, in terms of % by weight, 0.85 to 1.10% of C, 0.10 to 0.70% of Si, 0.20 to 0.60% of Mn, 0.10 to 0.60% of Cr, 0.005% or less of Al and optionally at least one member selected from 0.10 to 2.00% of Ni and 0.10 to 3.00% of Co with the balance Fe and unavoidable impurities and, provided thereon, a brass plating, the steel wire having a diameter of 0.1 to 0.4 mm and a tensile strength of 400 kgf/mm.sup.2 or more, the surface of the brass plating being provided with indentations having a depth of 2 .mu.m or less at intervals of 50 .mu.m or less in a percentage area of indentations of 10 to 80%; and a process and apparatus for producing a high strength, ultra fine steel wire, comprising subjecting a steel wire material to a patenting treatment, brass plating and wire drawing and subjecting the steel wire material to a shot peening treatment in an air blast system while applying a tension to the steel wire material.