The invention has a step where a transmitting station in a second radio communication system determines whether transmission of a second radio communication system signal using a shared frequency band is possible or not based on load information of a first radio communication system broadcast from a base station in the first radio communication system, a step where the transmitting station in the second radio communication system calculates predicted interference power caused in a receiving station in the first radio communication system by the second radio communication system signal transmitted using the shared frequency band, and a step where the base station in the first radio communication system increases an allowable interference level of a first radio communication system signal transmitted using the shared frequency band based on the predicted interference power broadcast from the transmitting station in the second radio communication system.