In deviation prevention support ECU 10 in driving operation support system 1, an applied torque by steering torque applier 17 is set based on a vehicle speed of a vehicle. The applied torque is set to increase with increase of the vehicle speed. An upper limit according to the vehicle speed is set for this applied torque. Furthermore, in a Start interval in application of the applied torque, a rate of increasing to reach a maximum is determined according to the maximum of the applied torque. In a Close interval, the applied torque is decreased at a rate different from that in the Start interval, and the absolute rate of increasing the torque in the Start interval is set to be larger than the absolute rate of decreasing the torque in the Close interval.