To obtain a less expensive steel cord excellent in rubber permeability and at the same time in buckling resistance, having high strength, high tenacity and excellent fatigue resistance and enabling an excellent rubber reinforcement with a small number of element wires.

This is a flat steel cord prepared by twisting three element wires. The constituting element wire is produced using carbon steel containing carbon in 0.80-0.85% as a raw material, and it has tensile strength Z of ≥-200d+400 before twisting into a cord and the ratio of an aggregate strength A of element wires before twisting to a cord strength B after twisting of ≥0.925.