Provided is an embolization coil in which even if the coil is wound in a shape of a small diameter, an elongation-preventing wire is not broken and the delivery property thereof can be prevented from deterioration. An embolization coil has a coil of partial or full-pitch winding and an elongation-preventing wire which are fixed respectively at two points different from each other, and is characterized in that the natural length of the coil arranged between two different points before the coil is fixed is longer than the length of the elongation-preventing wire arranged between two different points before the elongation-preventing wire is fixed.