We present preliminary results of our spectropolarimetric observations of the X-ray binary Cyg X-1 with FORS1 at the VLT/Kueyen (Paranal, Chile). This is the first successful attempt to detect a magnetic field in a binary system with a black hole. The mean longitudinal field over the disc of the optical star (09.7Iab supergiant) varies regularly with the orbital period phase reaching 130 G (sigma = 30 G) at phase 0.4. Measurements based on the Zeeman-effect were conducted using the total of the supergiant photospheric spectrum absorption lines. Similar measurements over the $HeII\lambda4686$ emission line yielded a field value of $\sim$600 G at 2-sigma level. The Doppler tomogram of the system based on the $HeII\lambda4686$ line profiles shows that the line emission component originates in the outer regions of the accretion structure. According to the standard model of the disc accretion, such numbers correspond to the near-Black-Hole magnetic field value of $\sim$10$^8$-10$^9$ G and can explain the Cyg X-1 X-ray millisecond flickering.