A numerical model of magnetic field structure in the presence of turbulent motions of the interstellar gas has been made. We solved the kinematic equation of magnetic field transport in a limited volume of ISM. Diffusion effects smoothing out small-scale structure are allowed as well. A permanent helical configuration of field lines has been found. This justifies, at least partly, searching solutions in the dynamo theory in the form of field modes. The presence of diffusion appears essential for the time evolution of magnetic field and magnetic energy density.