In the coil spring of the present invention, a helical space defined by a space between coils has a first end region whose space is increased as it extends towards the other side in the axial direction from a first reference point where the space is zero, a reference region whose space is set at a reference value L (L>0), and a second end region whose space becomes narrow as it extends toward the other side in the axial direction and zero at a second reference point. The first end region is configured such that the number of turns of the helical space is greater than 1 and the space between coils in a terminal position is greater than the reference value L. The helical space has a first transitional region between the terminal position of the first end region and the reference region, the first transitional region being configured so that the distance of space between coils is reduced from the terminal position of the first end region along the helical shape of the helical space toward the other side in the axial direction and becomes the reference value L.