Design method of a robust impedance control is proposed for the kinematically redundant manipulators. To achieve this objective, we first use the momentum feedback disturbance observer(MFDOB) scheme which can handle the nonlinear dynamics of a manipulator in Joint space. An extended task space formulation to describe the behaviors of task and null spaces of redundant manipulator is employed. Using the extended task space formulation and disturbance observer scheme, a robust impedance control method is designed. The performance of the proposed extended impedance controller is verified through experiments with a planar three links direct-drive manipulator.