The present lane departure prevention system can prevent a vehicle from departing from a lane of travel, even when the vehicle tows a towed vehicle. When the towed vehicle is detected, the lane departure prevention system changes a target yaw moment from that used in normal departure avoidance control operation. The change is based on a force input to the vehicle from the towed vehicle, which is caused by carrying out departure avoidance control, thereby controlling the vehicle so as not to depart from the lane using a corrected yaw moment.