Abstract: Rovings 30A and 30B as drafted are, under a parallel condition, passed through a collector 16, twisted and wounded from front rollers 12-1 and 12-2. A core yarn 34 is, via a guide member 40 as a snail wire, introduced into rovings 30A and 30B from the rear side of the front rollers. Since the guide member 40 is fixedly connected to the collector 16, the guide member 40 can follow with the lateral displacement of the collector 16, so that a central feed of the core yarn 34 to the rovings 30A and 30B is maintained, thereby always keeping a condition that the core 34 is fully covered by the outer fibers.