A decision is made as to whether a radio base station acting as an interference source is present in a macrocell or microcell, so that the interference from a mobile station transmitting high power can be presented in advance. The base station inserts its transmission power value of a forward broadcast channel into broadcast information. A newly installed base station C, receiving a forward frequency band, measures the received level of the broadcast channel, and captures the transmission power value. When the transmission power value is large, the threshold value is reduced (THRb), and when the transmission power value is small, the threshold value is increased (THRa). If the received level L is less than the threshold value, a decision is made that the channel is available.