PURPOSE: To produce a steel cord, having a rectangular cord cross-sectional shape and the angle of the wire from the cord longitudinal direction different between the positions of a short side and a long side, excellent in shape stability and rubber penetrability and capable of prolonging the tire life.

CONSTITUTION: This steel cord for reinforcing a rubber is obtained by forming an open cord prepared by loosely laying 3-9 wires or strands through a group of fluted forming rollers into a square cross-sectional shape and further working the laid cord into a flat shape. Thereby, the circumscribed shape of the cross section at right angles from the cord longitudinal direction is a rectangular form having rounded four corners and the cross-sectional shape has no twist in the cord longitudinal direction. The steel cord is formed so that the angle of the wire or strand from the cord longitudinal direction may be different at the positions of the short side and long sides to satisfy 1.05≤cosecα/ cosecβ≤2.00 (α and β are each the angle of the wire or strand from the cord longitudinal direction at the positions of the short side and long side of the cord cross section). The steel cord is used in any of a belt part, a carcass part and a part of a chafer part to produce a tire.