1. A driving assistance system for a primary vehicle, said driving assistance system comprising: an electronic image sensing device, for obtaining an image of an area behind and next to the primary vehicle, wherein the area includes a lane other than a lane occupied by the primary vehicle, said electronic image sensing device operable to obtain an electronic image of an enhanced area including a portion located outside of a normal range of view of a driver of the primary vehicle; an electronic display device for displaying the electronic image obtained using the image sensing device in a manner such that the electronic image is visible to a driver of the primary vehicle; and a mark display device for superimposing a mark on the image on the electronic display device, wherein the mark indicates a degree of danger with respect to a secondary vehicle running on the other lane when the primary vehicle enters the other lane, and the mark is a guideline for the driver of the primary vehicle to judge the distance between the primary vehicle and the secondary vehicle.