In a travel supporting control system 10 including an LDW/LKA system 17 which performs traveling-lane keeping assist control so that a vehicle V travels without deviating from the lane along which it travels, the LDW/LKA system 17 calculates a virtual lane width W, which is the width of the lane narrowed by an obstacle O detected by an obstacle detecting sensor 11, and stops the traveling-lane keeping assist control when the calculated virtual lane width W is so narrow as to be equal to or smaller than a threshold value and an avoidance operation of the driver is required. Accordingly, since the operation of LDW or LKA can be stopped at a proper timing, it becomes possible to prevent interference between the operation of the driver and the operation of the system for keeping the lane.