An automatic gain control circuit for controlling the gain of a variable gain amplifier block includes a count control signal generating block, an up-down counter, a gain control signal generating block, and a downcount clock signal generating block. The up-down counter upcounts an upcount clock signal or downcounts a downcount clock signal according to a count control signal generated by the count control signal generating block. The gain control signal generating block generates a gain control signal corresponding to a count value of the up-down counter. The downcount clock signal generating block generates a downcount clock signal whose frequency corresponds to the count value of the up-down counter.