An antenna beam scan unit includes: a Rotman lens that performs power division and synthesis between plural antenna ports and three or more beam ports; plural antenna elements which are connected to the respective antenna ports and to or from which radio waves are inputted or outputted; plural amplifiers that are connected to the respective beam ports of the Rotman lens and perform amplitude modulation on a signal; input paths for a transmission signal disposed in association with the amplifiers; switches for switching the input paths; and a beam control unit. The input paths include first paths and second paths on which a signal that is out of phase with a signal on the first paths is produced. The beam control unit selects two adjoining beam ports, and can switch the first paths and second paths as the input paths for the two beam ports.