The present invention prevents execution of a detour route search, responsive to and in accordance with received VICS data, where certain conditions are not met. To this end, the system of the invention calculates a time RT1 required for a vehicle to move from its present location to a first point where the vehicle must turn to the right or left to follow a previously determined guidance route and also calculates a time CT required to conduct a route re-search based on the received VICS data. If RT1.ltoreq.CT the system then performs a route re-search based on the received VICS data. On the other hand, if RT1