A reverse-swing type electron gun has been developed for use in an Automatic Beam Optimizer (ABO) system. The ABO was designed to discharge highlighted parts on a target. However, if the standard-type ABO system employs an RS type electron gun, the ABO circuit becomes a positive feedback loop giving rise to oscillation. Thus was the actual cause investigated of this oscillation in prior art systems, and measures have been developed for eliminating these defects. This paper presents the fundamental contorol characteristics of this new ABO system.