We developed the method for the investigation of the structure of the magnetic field in single sunspots from measurements of its line-of-sight component. On the basis of the study of 56 observational series for the longitudinal magnetic field and brightness in 8 single sunspots it is found that the magnetic axis of the magnetic force lines of a single sunspot is inclined at 8—10° to the west and at 1—5° to the north. The value of the inclination angle does not depend on the latitude in which a sunspot is situated. The beam angle of the magnetic field lines in a sunspot is determined. The sunspots located near the equator have the smallest values of the beam angle in an umbra. The beam angel of the magnetic field lines in a sunspot umbra increases as the latitude increases. The largest value of the beam angle is reached for sunspots located in latitudes of 15—25° and decreases for the sunspots for placed in latitudes of 25—45°. We discuss our results briefly.