A coil spring having a spring wire formed into a helical shape from a first end portion on a first side in an axial direction toward a second end portion on a second side in the axial direction, the coil spring including a first end coil part that has a first bearing surface facing to the first side in the axial direction and extends along a circumferential direction from an outer end portion in the axial direction forming the first end portion toward an inner end portion on the second side in the axial direction, a second end coil part that has a second bearing surface facing to the second side in the axial direction and extends along the circumferential direction from an outer end portion in the axial direction forming the second end portion toward an inner end portion on the first side in the axial direction, and a central coil part extending along the helical shape from the inner end portion of the first end coil part toward the second side in the axial direction and connected to an inner end portion in the axial direction of the second end coil part, the coil spring having a displacement length toward the second side in the axial direction of the first end coil part from the outer end portion until the inner end portion set to the thickness (a) of the spring wire so that a space between the outer end portion of the first end coil part and an inner end portion on the first side in the axial direction of the central coil part is zero, and a displacement length toward the second side in the axial direction between the outer end portion of the first end coil part and a point away along the circumferential direction from the outer end portion toward the inner end portion of the first end coil part by a half of turn around the axial line less than a half of the thickness (a) of the spring wire, characterized in that a relationship of the displacement length in the circumferential direction from the outer end portion toward the inner end portion of the first end coil part relative to the displacement length in the axial direction from the outer end portion of the first end coil part toward the second side in the axial direction is defined by a curved line that is opened upward. a displacement length toward the second side in the axial direction of the first end coil part from the outer end portion until the inner end portion set to the thickness (a) of the spring wire so that a space between the outer end portion of the first end coil part and an inner end portion on the first side in the axial direction of the central coil part is zero, and a displacement length toward the second side in the axial direction between the outer end portion of the first end coil part and a point away along the circumferential direction from the outer end portion toward the inner end portion of the first end coil part by a half of turn around the axial line less than a half of the thickness (a) of the spring wire, characterized in that a relationship of the displacement length in the circumferential direction from the outer end portion toward the inner end portion of the first end coil part relative to the displacement length in the axial direction from the outer end portion of the first end coil part toward the second side in the axial direction is defined by a curved line that is opened upward.