A non-circular cross-section coil spring, wherein a spring wire having a non-circular cross-section shape is coiled into such configuration that a major diameter of the cross-section is directed in the direction intersecting with a center line of the spring. Torsion is preliminarily given to at least a part of the spring wire so that the coil spring inner circumferential surface side of the above-mentioned major diameter may be deviated to a free end side of the spring with reference to the reference plane of extension and contraction of the coil spring in the case where the coil spring is a compression coil spring, but to the side of the aforementioned reference plane of extension and contraction in the case where the coil spring is a tension coil spring. In a coil spring comprising a larger pitch portion and a smaller pitch portion, a large angle of torsion is preliminarily given to the larger pitch portion and a small angle of torsion is preliminarily given to the smaller pitch portion. Upon application of a load, an angle of torsion of the spring wire becomes zero or nearly zero, thereby increase of the maximum shearing stress generated at the inner circumference of the coil spring can be suppressed, and also sharing stress in the spring wire can be made uniform.