The advent of humanoids has brought new challenges in the real-world application. As a part of ongoing efforts to foster functionality of the robot accommodating a real environment, this paper introduces a recent progress on a door opening task with our compliant humanoid, CoMan. We presents a task-prioritized impedance control framework for an upper body system that includes a dual-arm, a waist, two soft hands, and 3D camera. Aimed to create desired responses to open the door, a novel stiffness modulation method is proposed, incorporating a realtime optimization. As a preliminary experiment, a full door-opening scenario (approaching to the door and reaching, grasping, rotating and pulling the door handle) is demonstrated under a semi-autonomous operation with a pilot. The experimental result shows the effectiveness and efficacy of the proposed impedance control approach. Despite of uncertainties from sensory data, the door opening task is successfully achieved and safe and robust interaction is established without creating excessive forces.