Abstract: An electron beam processing apparatus imparted with capability of preventing occurrence of a failure in welding or the like processing of a workpiece by automatically compensating for changes in a focused position of an electron beam ascribable to time-dependent consumption of a rod-like cathode. The apparatus includes a bias voltage detecting circuit for monitoring a bias voltage applied to the rod-like cathode electrode and an automatic lens-current correcting circuit for controlling lens currents flowing through focusing coils by referencing experimentally obtained relations between the bias voltage or cathode temperature and lens current such that change of the position of the focal point can be nullified.