A radio base station (100) is provided with a stream determination unit (141) for determining whether communication quality of a radio communication channel between the radio base station (100) and a receiving device is lower than a predetermined threshold, and an antenna selector (142) for selecting, from among transmitting antennas (131-134), transmitting antennas such that the distance between the transmitting antennas (131-134) becomes shorter than that before the communication quality is determined to be lower than the predetermined threshold when the communication quality is determined to be lower than the predetermined threshold.