A radio base station 100 includes fading rate measurement units 103a to 103n configured to measure a fading rate of a radio signal for each of the antenna elements 101a to 101n, the radio signal being received through the antenna elements; and a reference signal calculator 105 configured to output a reference signal used in an adaptive control of the directivity of the array antenna 101. The reference signal calculator 105 outputs the reference signal on the basis of a plurality of fading rates measured by the fading rate measurement units 103a to 103n.