<p>An alignment control system using beam-tilting 1-D arrays for a 120-GHz-band corporate-feed 2-D waveguide-slot array antenna is presented. The 2-D waveguide-slot array antenna transmits data, and the 1-D arrays are used to determine array alignment. We design two types of 1-D array antenna and fabricate a corporate-feed 2-D waveguide-slot array antenna surrounded by four beam-tilting 1-D arrays. We then construct an alignment control system and evaluate the performance of the control. We find that the angular accuracy of the antenna alignment control was within ±1deg.</p>