Abstract: An automatic gain control circuit for a satellite communication transmitter, comprising a gain amplification circuit for amplifying an intermediate frequency signal from an output terminal of a modulator in the satellite communication transmitter, a distributor for distributing the amplified intermediate frequency signal from the gain amplification circuit, an intermediate frequency signal detector for detecting the intermediate frequency signal distributed by the distributor, a reference signal detector for detecting a reference signal from an indoor system controller, the reference signal being used to control a level of the intermediate frequency signal distributed by the distributor, and a differential integrator for offsetting variations in an output signal from the intermediate frequency signal detector and in an output signal from the reference signal detector based on external temperature variations with respect to each other and feeding the resultant signal back to the gain amplification circuit.