Abstract: In a satellite communication system in which a satellite repeater and a transmission channel are shared between a plurality of earth stations for satellite communication, each of the earth stations stops the initiation of the transmission of the transmission signal upon detection of a reception signal via a reception channel corresponding to a transmission channel of the station. On the other hand, if the reception signal is detected during the transmission of the transmission signal, the earth station continues the transmission of the transmission signal until a predetermined transmission of the transmission signal is completed.