A reception side radio station has a notification signal generator 108 which transmits a notification signal for notifying information of a frequency of a radio link being used at the radio station, and a transmitter 111 which transmits information indicating a reception power level and its frequency as radio signal data. On the other hand, a transmission side radio station has a notification signal measurer 106 which measures a reception power level of the notification signal and detects the frequency notified by the signal, and a frequency band controller 109 which determines an assignable frequency band for a radio link between the transmission side radio station and the reception side radio station based on the radio signal data and the notification signal.