A gain control circuit for an amplifier having a stepwise variable gain is disclosed, which includes a peak detector detecting and holding a peak value of an output voltage of the amplifier, a reference voltage generator generating first and second reference voltages having values different from each other, a comparator circuit comparing the peak value with the first and second reference voltages, and a control circuit responding to a comparison output derived from the comparator circuit and controlling the gain of the amplifier one step by one step such that the peak value becomes to intervene between the first and second reference voltages. When the peak value exists between the first and second reference voltages, the control circuit holds the gain of the amplifier at the current value, so that the amplitude of the output voltage is controlled to be substantially constant.