[en] A development of the polarimeter system for measuring the azimuthal magnetic field in the plasma focus (PF) device is presented. Measurements were carried out on the PF-360 device by means of the Faraday rotation (FR) method. It was concluded that current-driven instability of plasma does not cause enhanced diffusion of the magnetic field to the moment when the MHD m=0 instability of the plasma column is observed. (author)