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.