To simplify an entire system without switching a filter characteristic, etc., of radio equipment for a control channel by switching so that control channel data may be sent to radio equipment for a conversation channel when a radio frequency of a control channel receives interference.

In an MCA system, when an interference is detected in a radio frequency of the radio equipment for a control channel, a main CPU 8 controls Do 7 and switches Cch Data to an approach I/F2-3 of S1ch. When an interference is still detected even with this, it further switches to an approach I/F2-4 of S2ch. With this, control channel data are transmitted through radio frequencies of the S1ch and S2ch and approach lines. A radio frequency of the control channels is continuously supervised after switching, and when interference is not detected any more and it is decided that it is recovered, the frequency of an original control channel(Cch) is automatically returned.