Abstract: Untwisted synthetic resin string comprising two rolled portions each spiral in cross section and formed by inwardly rolling toward each other the opposite side edges of a strip of thermoplastic resin film stretched at least longitudinally thereof. The rolled portions extend longitudinally of the string in parallel with each other and are partially adhered together longitudinally thereof. Also disclosed are an apparatus for manufacturing the untwisted string from a strip of thermoplastic resin stretched at least longitudinally thereof and another apparatus for manufacturing an untwisted string having a single rolled portion from like resin strip.