To easily and precisely provide a single-ply twisted steel cord for reinforcing a rubber product, having sufficient penetrability of rubber and excellent fatigue resistance.

The steel cord 10 has a single-ply twist of 1×n (n=3-6) and comprises normal filaments (wire 12) having no kink except the spiral kink for cord twist, and spiral filaments having small spiral kinks separated from the spiral kinks for the cord twist. The spiral filament is regulated so that when the spiral cord after untwisting is arranged horizontally, the maximum value of the angle formed by the tangential line t2 of a locus projected on the horizontal plane on the projected plane, and the base line r2 of the spiral kink for the cord twist may be 1.2-2.0 times as much as the twisting angle of the cord.