PURPOSE: To make a base station small and to simplify the circuit configuration by adopting configuration comprising a transmission power amplifier and a reception common amplifier only for the base station.

CONSTITUTION: A center station 10 is provided with a modulator MOD applying PSK modulation to transmission data sent to plural mobile stations 30 subscribing to the system to obtain a radio frequency signal f0 and with a demodulator DEM receiving a radio frequency signal subject to PSK modulation from the plural mobile stations 30 to obtain reception data. Thus, the equipment configuration of the base station 20 is simplified and made small in size. Then a reception level discrimination circuit 1 provided in the base station 20 compares a level of a reception signal of plural speech channels different from each other from the mobile station 30 with a reference level R to activate a switch 2, which turns on/off an input signal from a polarity inverter 3. When the switch 2 is closed, an outgoing signal from a center station 10 is branched to a synthesizer H and a signal whose polarity is inverted is outputted.