A coil spring has a spring wire wound in a coil shape having an outer diameter side portion and an inner diameter side portion on a peripheral shape in a cross section thereof, one of the outer diameter side portion and inner diameter side portion formed in a semi-circular shape expressed by x2+y2=b2, the other thereof formed in a non-circular shape with a long diameter “a” and a short diameter “b” expressed by (x/a)α+(y/b)α=1, and value of the “α” set in a range of 1.85 to 2.45, and contact faces provided between the inner diameter side portion and the outer diameter side portion on the peripheral shape in the cross section such that each contact face comes into contact with a contact face of an adjacent coil in an axial direction along an axis line of the coil spring.