Abstract: A spiral double-twisted structure is provided having an n-th upper steel wire (An) and an n-th lower steel wire (Bn) which are paired with each other and rotated in one direction to form a front spiral twisted structure having a plurality of twists. Further, a k-th transverse steel wire (Ck) may be transversely inserted between the n-th upper steel wire (An)and the n-th lower steel wire (Bn)of the front spiral twisted structure. Additionally, the n-th upper steel wire (An) and the n-th lower steel wire (Bn) may be rotated in a direction opposite to the one direction after passing over the k-th transversr steel wire (Ck) serving as a centerline, in order to form a rear spiral twisted structure having a plurality of twists.