In the stretching mentioned above, extruded fibers may be stretched at a stretching ratio of less than its natural draw ratio (NDR) to form thick-and-thin hollow fibers in which unstretched thick portions and stretched thin portions exist in a mixture. In this case, while it is possible to form slits in both thick portions and thin portions, more slits can be formed in the thick portions than in the thin portions by adjusting the conditions of a chemical treatment for dissolution as suitable since the orientation degree is particularly low in the thick portions. When slits are selectively formed in the thick portions, physical properties of the fiber including abrasion resistance (fibrillation resistance) and others are further improved, since the "scroopy feeling" is more emphasized and a resistance to external stress is increased.