PURPOSE: To eliminate the fluctuation of attenuation by adding a control circuit of a feedback loop with a control signal separately from an input signal to a variable attenuator composed of a variable attenuator element whose attenuation is fluctuated due to cause to fluctuation.

CONSTITUTION: An input signal desired to be attenuated by a variable attenuation circuit is fed to a signal input terminal 1 and a control signal having a different frequency band form the input signal is generated from a signal oscillator 2, after the input signal and the control signal are added by a coupler 3, the result is attenuated by an attenuator 4. Since feedback loops 7∼13 are constituted for the control signal, when the loop gain is sufficiently large, the control voltage and the rectified voltage of the control signal are made nearly equal to each other. When the amplifiers 8, 12 and a rectifier 9 for the control signal are stable after the separation, the control signal level at the separating point of the output of the variable attenuator corresponding to the control voltage is controlled stably and the input signal is also made to stable output level through the variable attenuator 4 controlled stably by the control voltage. Thus, the stable variable attenuation circuit independently of the fluctuation is obtained.