Abstract: In the process of drawing/heat treating synthetic fiber thread melted and spun via a plurality of godet rollers and subsequently winding the same, accumulation of extraneous matter on the surface of the godet rollers may be prevented by performing multistage drawing/heat treatment while reciprocating the thread in the direction of the axis of rotation of the godet roller using the godet rollers at least two of which have surfaces having the roughness of 0.5≦Ra≦5 and one of which has a surface at a temperature of at least (melting point of synthetic fiber−70° C.), whereby occurrence of thread breakage or generation of fuzz may be prevented and synthetic fiber whereof the rate of operation can be increased and efficiency of manufacture is improved may be obtained.

Abstract: Disclosed is a polyethylene terephthalate untwisted multifilament which satisfies the following requirements (A), (B), (C) and (D);(A) the intrinsic viscosity [IV] is 0.97 to 1.15;(B) the amorphous orientation function [fa] is not larger than 0.55;(C) the tenacity [T] (g/d), the shrinkage [.DELTA.S] (%) as measured after standing in dry air at 150.degree. C. for 30 minutes, the medium elongation [ME] (%) under a load of 4.5 g/d, and the dimensional stability index [Y] expressed by the formula: Y=ME.sup.0.81 +.DELTA.S+1.32 are within ranges defined by the following formulae (a), (b), (c), (d) and (e):0.33Y+5.55.ltoreq.T.ltoreq.0.33Y+6.50 (a),8.0.ltoreq.T.ltoreq.9.5 (b),8.5.ltoreq.Y.ltoreq.10.5 (c),5.ltoreq.ME.ltoreq.10 (d),and2.ltoreq..DELTA.S.ltoreq.g (e);and (d) the elongation at break is at least 11% and the product of the tenacity and elongation, which is defined by: ##EQU1## is 30 to 36.