In a legged mobile robot control system having leg actuators each driving the individual legs and arm actuators each driving the individual arms, an external force acting on the right arm is detected, operation of the right arm actuators is controlled to produces a handshake posture, and operation of the leg actuators is controlled based on the detected external force acting on the right hand during handshaking, thereby improving communication capability by enabling it to shake hands with humans and to maintain a stable posture during the handshaking.