To provide a crosstalk warning device that warns occurrence of crosstalk in a mobile communication system employing a broadband frequency.

An antenna 11 and an antenna changeover device 12 receive a crosstalk disturbing wave and a disturbing wave monitor receiver 13 detects a reception frequency and signal strength of the crosstalk disturbing wave. A controller 14 selects a signal in excess of a setting threshold value as a disturbing wave and gives transmission frequency information and a start signal to a warning wave transmitter 15. The warning wave transmitter 15 uses the start signal to transmit a warning wave with the same frequency as that of the crosstalk disturbing wave.