To provide artificial hair fiber retaining heat resistance and fibrous physicality such as strong ductility, and having luster, appearance and touch near to those of human hair.

The artificial hair fiber which is obtained by subjecting thermoplastic resin to melt spinning has 1-50 mm cycle of fineness change in a fibrous flow direction. The artificial hair fiber is given fineness change at a prescribed cycle in the fibrous flow direction to present nonuniformity like human hair, and express luster, appearance and touch similar to those of human hair.