A driving assistance system designed to accelerate or decelerate according to the speed set by a driver with an aim to relieve a driver of fatigue. Since CC does not apply braking for deceleration, the system enables driving at a higher speed than a set speed on a downhill. CC is deactivated when a driver presses CANCEL switch or steps on a brake. However, CC does not consider forward vehicle's relative location or speed, the driver should pay attention to traffic condition in the front at all times.