A posture control system for a mobile robot. When an unexpected external force acts, the system is configured to control and stabilize the posture of the robot driving an arm link such that, in response to a first external force that is a component in a predetermined direction of an unexpected external force, a second external force acts on the arm link in a direction orthogonal to the predetermined direction. With this, when the mobile robot receives a reaction force, even if the posture becomes unstable or the robot receives an unexpected reaction force, it becomes possible to preserve the dynamic balance and to maintain a stable posture.