A drive assist system of a vehicle for preventing a lane moving-out includes a pair of CCD cameras for taking picture images of the scenery in front of the vehicle, an image processing section for processing the picture images, a road/object detecting section for obtaining image data, a lane moving-out judging section for judging a lane moving-out from a lane, a roadside judging section for issuing an alarm when it judges a lane moving-out in the roadside direction, a moving-out direction obstacle judging section for issuing an alarm when there is a possibility of colliding with an obstacle on a moving-out direction lane, a lane width judging section for stopping or suppressing an alarm in case where the lane moving-out is an avoidable behavior due to the narrow width of the lane and a front direction obstacle judging section for stopping or suppressing an alarm in case where the lane moving-out is for avoiding an obstacle in front of the vehicle.