Coil spring

A coil spring comprising a wire rod having a first end and a second end, the coil spring comprising:

• a first end turn part including the first end of the wire rod;
• a second end turn part including the second end of the wire rod;
• and
• an effective spring part which comprises a plurality of coil portions formed between the first end turn part and the second end turn part, and which has a gap provided between each pair of two adjacent coil portions among the plurality of coil portions,
• wherein the wire rod comprises:
• a round section portion, a first section of the round section portion taken perpendicular to a length direction of the wire rod being round;
• a square section portion provided from the first end of the wire rod over a length of the first end turn part, the square section portion having at least 2.0 turns, the square section portion comprising at least a first coil portion and a second coil portion, the square section portion further comprising a contact portion in which the first coil portion contacts with the second coil portion in a state in which the coil soring is compressed, a second section of the square section portion taken perpendicular to the length direction being substantially square, a length of each side of the second section being no greater than a square root of ½ multiplied by a diameter of the wire at the round section portion, the second section being constant in the length direction, and lengths of the four sides of the second section being equal to each other within a range of tolerance in terms of processing;
• and
• a taper portion provided between the round section portion and the square section portion, the taper portion having at least 1.0 turns, a third section of the taper portion taken perpendicular to the length direction changing from a round shape to a substantially square shape, and a sectional area of the third section decreasing from the round section portion to the square section portion.