The lamellas narrowing device is used for feeding in of wide fabric / lamellas of the vertical blind, trimming it to the desired dimension and rewinding it onto a reel. The cutting process itself is carried out with a simple knife (easily available in any hardware store or multi-dicipline store) during the process of winding the fabric . The device is extremely easy and safe to use. In case of difficult fabrics instead of a regular knife, it is possible to use an ultrasonic knife, which prevents the fabric from fraying. The construction of the narrowing device is made of system profiles. Even cut and precise winding of the fabric are guaranteed by the tensioning roller. The position of the knife is adjustable, so the width of the fabric to be cut is also adjustable. The ability to purchase a wider vertical blind tape and cut it to the correct size, saves on outsourcing this task to an external company and extends the purchasing possibilities of the manufacturer.