To improve the durability of detachment and attachment strength by forming of polytrimethylene terephthalate fibers.

The polytrimethylene terephthalate fibers are polyester fibers whose repetition unit is trimethylene terephthalate and contain the trimethylene terephthalate unit of about 50 mol.% or higher, preferably 70 mol.% or higher, more preferably 80 mol.% or higher, further preferably 90 mol.% or higher. Therefore, polytrimethylene terephthalate containing the total amount of other acid components and/or glycol components as the third component, of about 50 mol.% or lower, preferably 30 mol.% or lower, more preferably 20 mol.% or lower, further preferably 10 mol.% or lower is also included. The polytrmethylene terephhalate is synthesized by bonding a tereththalic acid or its functional derivative, and trimethylene glycol or its functional derivative under appropriate reaction conditions in the presence of a catalyst.