Recently, robots are expected to support actions performed in a real-life environment in our daily lives. However, robots encounter several interferences while performing physical interactions, such as shaking hands, hugging, and holding various objects. Therefore, it is difficult for the robots to perform such actions flexibly owing to the unexpected noises associated with these actions. Humans, in contrast, can cope with various disturbances thanks to the flexibility of their body structure. It is suggested that this property can be realized by changing the passive dynamics depending on the situation and task. Passive dynamics can be changed using two important mechanisms. One is imparting a high degree of freedom, i.e., redundancy of joints. The other is to incorporate a multi-articular muscle, i.e., redundancy of actuators. Using these redundancies, several complicated movements and power adjustments can be realized. In this study, a human-like upper-body musculoskeletal robot comprising redundant joints and actuators is developed. The robot can change its passive dynamics by simply changing the mutual interconnection of air actuators. In this paper, we report the structure and performance evaluation of the robot. The response characteristics of the robotic arm under different combinations of actuators connections are presented.