Disclosed is an automatic gain controller capable of reducing signal saturation or signal distortion caused by out-of-band signals of a filter extracting an object signal or delay of a control signal and capable of precisely measuring a signal level in a filter band. An AGC response control section compares a level of control voltage ("V2_I terminal" signal) outputted from a first AGC control section and inputted into a "V2_I terminal" with a level of control voltage ("V3_I terminal" signal) outputted from a second AGC control section and inputted into a "V3_I terminal". If the control voltage, which is the "V3_I terminal" signal, outputted from the second AGC control section is less than the control voltage, which is a "V2_I terminal" signal, outputted from the first AGC control section, the AGC response control section controls an AGC amplifier by using the control voltage outputted from the second AGC control section. If the control voltage, which is the "V3_I terminal" signal, outputted from the second AGC control section is greater than the control voltage, which is the "V2_I terminal" signal, outputted from the first AGC control section, the AGC response control section controls the AGC amplifier by using the control voltage outputted from the first AGC control section.