In this paper, we analyzed the gait support procedure of the lower limb's disturbance by our proposed gait support robot "Walk-Mate". "Walk-Mate" is a virtual locomotion robot, which supports the handicapped gait motion by presenting acoustic rhythmic stimuli controlled dynamically by its user's gait motion. We focused on the hemiplegia of lower limb and measured improvement of bilateral asymmetry with Walk-Mate's support. As the results, we found that the improvement procedure is realized by following characteristic two mechanisms; Short-term control with about 10 seconds of timescale for the improvement of the phase characteristics of the footstep rhythm and Long-term control with about a minute of timescale for the improvement of the complexity of gait motion pattern. Therefore the result suggests that Walk-Mate's rhythmic control mechanism is effective to improve the gait disturbance, from the viewpoints of the rhythm and complexity of gait, and that the improvements are realized by a two-level hierarchical control mechanism in interaction with the dynamic environment. © 2007 IEEE.