A communication unit includes a plurality of antennas and controls, in transmitting signal using the plurality of antennas, the transmission directivity of the plurality of antennas based on a known signal from the communication terminal. A radio resource allocation unit allocates, to the communication terminal, an uplink frequency band for use in transmission of the known signal from a plurality of unit frequency bands lined in a frequency direction. In newly allocating the uplink frequency band to the communication terminal, the radio resource allocation unit newly determines the uplink frequency band based on elapsed time since the last use of the unit frequency band as the uplink frequency band.