A concrete reinforcing metal fiber capable of being easily and uniformly dispersed in concrete. The metal fiber integrally includes a longitudinal strength body which bears tensile force that works thereon, and two rows of intermittent fins extending on the opposite sides of the strength body. The flatness ratio, namely, the ratio of the maximum width of the metal fiber to the maximum thickness of the same, of the metal fiber is in the range of 2.5 to 6.