A subject vehicle runs under a fixed speed travel at a target speed by an auto-cruise system. When it is determined that the subject vehicle cannot arrive at a destination using a present residual fuel quantity, a navigation apparatus is caused to retrieve an eco-route. It is then determined whether the subject vehicle can arrive at the destination by running the eco-route at a fuel-efficient speed which can consume fuel efficiently using the present residual fuel quantity. When it is determined that the subject vehicle can arrive, the fuel-efficient speed is presented as a recommended speed. Thus, a driver of the subject vehicle is urged to designate the fuel-efficient speed as a new target speed for the auto-cruise control.