To solve the problem of quality, lack of shape stability and bulkiness, etc., of two-dimensional wrinkle or crimp of a zigzag folded structure imparted by the heat and pressure in a stuffing box to a string-like or tape-like thermoplastic fabric or yarn, and caused by unevenness of heat and pressure in the stuffing box, by a conventional pushing-in method.

This method for producing the wrinkling processed yarn comprises allowing a hollow cylindrical fabric into which a metallic introducing core connected to a metallic introducing widening spherical head is inserted, to pass in a noncontact hollow heating tube mounted between two pairs of rollers with grooves to stably heat-set bellows-like staying wrinkles caused by the difference of surface speeds of the two pair of the rollers as a means for providing three-dimensional bulkiness while keeping the hollowing structure by using the hollow cylindrical fabric obtained from a thermoplastic synthetic fiber as a base material, and uniformly and stably imparting the three- dimensional folded wrinkles in concentric bellows-shape along the hollow center line thereto as shown in fig. 1.