In a legged mobile robot having at least a body and a plurality of legs each connected to the body through a first joint and a foot each connected to a distal end of each of the legs through a second joint, a floor reaction force detector is installed between the second joint and a contact end of the foot. More specifically, an upper portion of the floor reaction force detector is connected at a location near the second joint, and the contact end of the foot or thereabout is constituted by a spring mechanism that is lower in rigidity than a member constituting the second joint or thereabout such that a lower portion of the floor reaction force detector is connected to the contact end through the spring mechanism. With this, it becomes possible to provide the floor reaction force detector that can improve detection accuracy of the floor reaction force and prevent the performance of control from being degraded, while enabling to maintain a stable posture during standing and to decrease the impact at foot landing.