An automatic gain control circuit controls a gain of a wireless receiver in accordance with an amplitude of a reception signal. The automatic gain control circuit includes a reference level calculator, a register, a reference level adjuster, and a bit width conversion circuit. The reference level calculator calculates a reference level on the basis of the amplitude of the reception signal. The register stores an adjustment value. The reference level adjuster adjusts the reference level on the basis of the adjustment value stored in the register. The bit width conversion circuit performs a bit width conversion for the entire amplitude direction by changing a bit pitch for determining discrete data values of the reception signal, on the basis of the adjusted reference level.