Automatic gain control circuit and method thereof and demodulation apparatus using the same

An automatic gain control circuit able to perform high speed and correct level acquisition, able to prevent occurrence of error, and able to prevent a crash of the system. An amplification gain controller outputs a gain control signal to an automatic gain control amplifier to amplify the received signal with maximum value when receiving a burst detection trigger signal. A second gain control signal based on the detected reception signal power is calculated when receiving a first burst synchronization detection signal; and this second gain control signal is output to the automatic gain control amplifier. A received digital signal is amplified with the second gain and integrated to find the reception signal power, from which a third gain control signal is calculated and outputted to the automatic gain control amplifier to amplify the received signal with this third gain.