A camera-orientation estimation unit estimates the amount of change in camera orientation on the basis of vehicle speed changes obtained from a vehicle-information acquirer. A distance-information update decision unit decides, on the basis of the amount of change in camera orientation, whether to update distance information by computing new distance information in a distance-computation unit or to update distance information using distance information stored in a distance-information memory unit. If the distance-information update decision unit has decided to update distance information by computing new distance information, a display device displays distance information that the distance-computation unit computes from a real-time image. If the distance-information update decision unit has decided to update using past stored distance information, the display device displays past distance information read from the distance-information memory unit.