To obtain steel fibers which make it possible to stably obtain high strength to bending, shearing and tension and enhance the anchor effect within concrete by imparting torsion to a flat wire which is an elongated plate having a rectangular shape in cross section.

Iron and steel materials which are the raw material for the steel fibers include iron, steel, stainless steel, mild steel, special steel, electric copper, cast steel and cast iron, etc. The amount of the steel fibers to be incorporated is 40 to 80 kg/m3 for, for example, tunnels, 60 to 80 kg/m3 for slopes of filling, etc., 40 to 100 kg/m3 for pavement, 30 to 40 kg/m3 for building slabs and 80 to 100 kg/m3 for concrete secondary products. The torsional pitch may be a pitch fixed over the entire length and the spacings between the respective twists may be varied. More preferably, the fiber dimensions are 30 to 100 mm length, 0.8 to 5 mm width, 0.1 to 1.0 mm thickness and 5 to 60 mm torsional pitch. The kinds of the concrete are not restricted. The concrete products are not restricted either. Such products are, for example, hume pipes, ditch lids, U-shaped ditches, etc.