Abstract: The present invention relates to an automatic frequency control device and an automatic gain control device which have the advantage of improving the efficiency of a system with very low signal-to-noise ratio by compensating for frequency error generated at the local oscillator of a satellite or on the receive paths by demodulating the modulated signal continuously sent out from a transmit earth station for transmitting information without using the separate pilot frequency at a receive terminal of a receive earth station and locking at local oscillator of a frequency downconverter to a voltage controlled oscillator tracking an error after detecting a phase error of a carrier by using demodulated data, by compensating the frequency error due to Doppler frequency deviation by locking a local oscillator of a frequency upconverter to a voltage controlled oscillator tracking a phase change according to Doppler frequency deviation included in the clock after recovering the clock from the demodulated data, and by c