To provide a coil spring that can properly control lateral force not only in a lateral direction of a vehicle body but also in a longitudinal direction via a simple structure when mounted in a strut suspension system.

A compression spring 5 is formed with a curved coil axis CA. The pitch of a lower end turn 5a is set so that the lower end turn 5a is inclined against a lower seat 4 at a given angle α in a direction to shorten an axial length inside the curvature, and/or the pitch of an upper end turn 5b is set so that the upper end turn 5b is inclined against an upper seat 3 at a given angle β in a direction to shorten an axial length outside the curvature. In a plane perpendicular to a plane including an end turn center axis OF of the upper end turn and the lower end turn and the coil axis CA, the pitch of the lower end turn is set to from an inclination of a given angle γ against the lower seat, and/or the pitch of the upper end turn is set to form an inclination of a given angle δ against the upper seat, and the coil axis is, if necessary, curved in a given direction.