The quality of flax products depends on the way of flax straw retting. Currently, the best and most widely used method of flax straw retting is way of dew retting. Flax stems are laid in a thin layer on the flax field where they were grown or on a clover or grass field. During the retting process, plants tend to grow through the flax swaths depending on the air temperature (starting from 18°C) and humidity (50­-60%). Therefore, the flax straw picking up process should be done with certain efforts, however, without damaging the stems. (Research purpose) To determine the bonding forces of the flax straw with the rettery (a flax field or a grass field). (Materials and methods) The authors have designed an instrument to measure and register the considered forces as well as a general mechanism of the flax straw picking up process, which operates in conjunction with the IP 264 (BS) measurement information system, and also developed a research methodology. This system is integrated with to a laptop with the pre-­installed «Testing» software. The system is adopted to use the MS Excel software to transfer data in MS Excel format for further plotting. (Results and discussion) It has been shown that the bonding forces of flax stems, their changing pattern, and the maximum value during the picking up process depend on the degree of penetration by grass plants into flax swaths and the grass plant density per square meter. (Conclusions) In process of picking up the grass-­penetrated swaths, they show weak strength characteristics for transportation and an increased tendency to break the continuity of their picking up. The values of the ratio of the translational speed of a pick-­up device and the rotary speed of a picking device fingertip can be greater than the value of the relative elongation at the point of pulling the swath away from the ground. The coefficient of strength to pick up the swaths from a clover rettery is higher than that of flax and grass retteries.