PURPOSE:To attain effective utilization by transmitting a voice from a mobile circuit to a control station while being attenuated at the selection of other radio base station at a radio base station and applying multi-drop connection to plural base stations on one line accommodated in the control station to improve the communication efficiency per one line. CONSTITUTION:A control circuit provided with a reception terminal 11, a transmitter input terminal 19, a reception output terminal 20 and a transmission terminal 23 is inserted between a receiver of a radio base station and the control station of the mobile communication system. A contact (b) of a relay B driven by a reception level matching amplifier 12 and a press signal receiver 13 is connected between the terminals 11 and 9. Moreover, an attenuator 21 short- circuited by a contact (c) of a relay C driven by an output of a selection memory circuit 16 and a transmission level matching amplifier 22 are connected between the terminal 20 and 23. Then the output of the receiver 13 and the selection signal receiver 15 controls relay contacts (a), (c) and the relay contact (b), the signal through the voice circuit from the mobile station is attenuated by the attenuator 21 at the selection of other base station at a base station to improve the communication efficiency per one line.