Abstract: In the course of welding an electron welding beam is regularly deflected by means of linearly growing pulses to an electrons pickup arranged as a Faraday beam trap. As the electron beam travels in the course of deflection, it crosses the slit in the Faraday beam trap, and a signal proportional to the diameter of a heating point emerges across the trap. Depending on variations in said signal respective to a preset value, the focusing of the electron beam is also varied. The automatic device for stabilizing the heating point diameter has an electrons pickup with a resistor across its output, said pickup being connected, via a converter, to a comparison circuit also coupled with a backup signal setter. The output of the comparison circuit is connected to the focusing coil of the electron beam gun for varying the focusing coil of the electron beam. For deflecting the electron beam, there is a generator of saw-toothed pulses, connected to the deflector coil of the above electron gun.