An electronic throttle valve control system prevents rapid rotation of a throttle valve reliably when the control system has a failure. A throttle valve controls the amount of intake air to an internal combustion engine, an electric motor drives the throttle valve, and a rotational speed reduction mechanism reduces the rotation of the electric motor to control the rotation of the throttle valve. An urging mechanism urges the throttle valve in the closing direction. An attenuation mechanism attenuates the speed at which the throttle valve is rotated in the closing direction by the urging mechanism when the control system has a failure. The attenuation mechanism is the electric motor in a regenerative mode or an air damper.