An artificial hair fiber is provided that is easy to curl or set. An artificial hair fiber is usually formed and processed within a temperature range from 90 to 150° C. The artificial hair fiber has a storage elastic modulus E′ in the formation temperature range. A ratio (E′90/E′150) of a storage elastic modulus E′ at a temperature of 90° C. to a storage elastic modulus E′ at a temperature of 150° C. is 3 to 20. By this means, the artificial hair fiber can be well curled or transformed, maintaining a desired dynamic characteristic without being melted. The artificial hair fiber can be formed and processed into such a curled hair, so that it is possible to provide a hairpiece product that meets the fashion needs of users.