The new motion control system described in this paper has an event-driven motion-module switching mechanism. This mechanism can select a previously prepared motion-module for each event generated from sensor information and can modify a reference input in real-time. This highly modular and extendable motion-compensating mechanism, especially effective in robot tasks with uncertainties and in robot motion that requires skill, should be useful for such robot tasks as machining and assembling. This paper describes the concept and implementation of the proposed system and presents some experimental results demonstrating its feasibility.