PURPOSE: To produce the subject fiber having excellent uniformity, dimensional stability and antistaticity in spite of high tenacity and high modulus and free from generation of scum by including a specific antistatic compound in a core component and specifying the thickness of the sheath component.

CONSTITUTION: The objective fiber having a modulus of 3-5g/d and a diameter of 25-55μm is composed of (A) a sheath component having a thickness of 7-20μm and (B) a core component containing 0.1-2.5wt.% (based on the monofilament) of a polyalkylene ether having a molecular weight of 800-20,000. The polyester used as a raw material for the fiber is preferably polyethylene terephthalate. The fiber is preferably produced by extruding the polymer through a sheath-core conjugate spinneret of an extruder-type melt-spinning machine, etc., applying a lubricant to the extruded fiber and drawing the obtained undrawn monofilament under heating.