This paper presents a novel Internet congestion control scheme, the active queue management (AQM) scheme, that supports transmission control protocol (TCP) flows and avoids serious congestion by suppressing bottleneck nodes. The proposed controller includes a proportional-derivative (PD) controller and a disturbance observer (DOB). PD control is performed to keep the queue length below the buffer size, and the DOB is implemented for robust congestion control. The DOB can estimate and compensate the variations in network parameters, e.g., the number of TCP connections. This paper also describes a design methodology of the proposed congestion controller including the PD controller and the DOB. The validity of the proposed method is shown by simulation results.