An antenna apparatus is installed in a base station in a code division multiple access communication system. The antenna apparatus comprises a plurality of antenna elements, each receiving a radio signal; a controller that produces an antenna control signal based on information contained in the radio signal received at each of the antenna elements; an adjusting unit that adjusts directivity characteristics of each of the antenna elements based on the antenna control signal; and an allocating unit that allocates the antenna elements to sectors based on the antenna control signal. The sector covers a portion of a cell controlled by the base station, and the number of sectors in the cell is variable by means of the antenna control signal.