To provide an apparatus which functions to manufacture effect yarn with a process machine by intentionally generating a plurality of shot lumps in the yarn by overfeeding the yarn in a short period of time, the apparatus comprising a servo-controlled yarn guide driven by a motor having an adjustable stroke and deflecting the yarn laterally.

A movement of a yarn guide (3) in one direction gives a little underfeed, the movement of the yarn guide in the other direction gives a significant overfeed. The yarn guide is mounted preferably by a wire rope, a string or a belt on a traverse movement element (2) formed of a flexible member rigid in the stroke direction, and driven thereby. The yarn guide is loop-shaped and provides a storage of a yarn length corresponding to a desired overfeed. The apparatus is used in a false-twisting machine and an air-texturing machine.