PURPOSE: To simultaneously use two or more terminal equipments in one earth station by providing a first modulating circuit for executing a modulation output by changing a transmission frequency band, and a second demodulating circuit for executing a demodulation by changing a demodulation synchronizing speed.

CONSTITUTION: A signal from an earth station 1 which has passed through a communication satellite 3 is received by a central control station 2, and a receiving signal is demodulated by a second demodulating circuit 22. When a line control circuit 25 receives a calling signal from other terminal equipment 11b than, for instance, a terminal equipment 11a in the earth station 1 being in the course of communication already, a synchronizing speed control circuit 32 leads out a demodulation synchronizing speed signal of two times and generates a line allocating signal so as to supply said signal to the second demodulating circuit 22. The first control signal extracting circuit 14 of the earth station 1 extracts the line allocating signal from in the demodulating signal and supplies it to the first modulating circuit and a modulation frequency band is doubled. In such a way, plural terminal equipments can be operated simultaneously without raising the transmission power.