A multi-beam satellite communication system comprising: - a relay apparatus mounted on an artificial satellite and adapted to relay communication of communication devices present in each of a plurality of beam areas; and - a control apparatus located on the ground adapted to control the relay apparatus , wherein the relay apparatus comprises: - a relay side receiving unit adapted to receive a relay signal to be relayed; - an analog relay unit having an analog circuit adapted to control a frequency bandwidth of the relay signal output by the relay side receiving unit , the analog relay unit being further adapted to output the relay signal whose frequency bandwidth is controlled; - a digital relay unit having a digital circuit adapted to control a frequency bandwidth of the relay signal output by the relay side receiving unit , the digital relay unit being further adapted to output the relay signal whose frequency bandwidth is controlled; - a relay side transmitting unit adapted to transmit the relay signal output; and - a relay side control unit adapted to cause the analog relay unit and the digital relay unit to output the relay signal, according to an analog relay unit control signal indicating a frequency band of the relay signal to be relayed by the analog relay unit and a digital relay unit control signal indicating a frequency band of the relay signal to be relayed by the digital relay unit , wherein the control apparatus comprises: - a control side communication unit ; and - a control side control unit adapted to generate the analog relay unit control signal and the digital relay unit control signal and to transmit the generated signals to the relay apparatus via the control side communication unit , wherein the control side control unit is adapted to monitor the relay apparatus and detect the received power density and when a received power density of the relay signal received by the relay apparatus is low, the control side control unit is adapted to generate a signal to relay the relay signal via the digital relay unit as the digital relay unit control signal, and the digital relay unit is adapted to amplify the relay signal indicated by the digital relay unit control signal in response to the digital relay unit control signal. - a relay apparatus mounted on an artificial satellite and adapted to relay communication of communication devices present in each of a plurality of beam areas; and - a control apparatus located on the ground adapted to control the relay apparatus , - a relay side receiving unit adapted to receive a relay signal to be relayed; - an analog relay unit having an analog circuit adapted to control a frequency bandwidth of the relay signal output by the relay side receiving unit , the analog relay unit being further adapted to output the relay signal whose frequency bandwidth is controlled; - a digital relay unit having a digital circuit adapted to control a frequency bandwidth of the relay signal output by the relay side receiving unit , the digital relay unit being further adapted to output the relay signal whose frequency bandwidth is controlled; - a relay side transmitting unit adapted to transmit the relay signal output; and - a relay side control unit adapted to cause the analog relay unit and the digital relay unit to output the relay signal, according to an analog relay unit control signal indicating a frequency band of the relay signal to be relayed by the analog relay unit and a digital relay unit control signal indicating a frequency band of the relay signal to be relayed by the digital relay unit , - a control side communication unit ; and - a control side control unit adapted to generate the analog relay unit control signal and the digital relay unit control signal and to transmit the generated signals to the relay apparatus via the control side communication unit , <EOS>