PURPOSE: To reduce operation restrictions/load on a ground station and an artificial satellite operator by automatically switching the transmission/reception power level in the communication system for artificial satellite to a level adapted to the other party of communication.

CONSTITUTION: The satellite bus system including a satellite bus-system transmission/reception antenna 1, a diplexer 3a, a satellite bus-system reception attenuator 4, a satellite bus-system transmission attenuator 5, a satellite bus- system receiver 7, a command decoder 8, a satellite bus-system transmitter 9, and a telemetry encoder 10 processes the distance and the direction of the other party of communication, which are obtained by satellite distance and direction measuring part 18, and reception power level information from the other party and controls the satellite bus-system reception attenuator and the satellite bus-system transmission attenuator 5 by an attenuator level control part 17 so that the reception level value calculated by these information coincides with a target design value. The same control is performed with respect to the satellite mission system.