A three-dimensional digital map prepared by an satellite or the like is stored in a first memory as a wide-area information. Narrow-area information obtained by a laser radar is stored in a second memory. Obstacle information on obstacles, such as high-voltage power lines, high buildings and cranes, is stored in a third memory. These three information are read out to generate virtual images on a see-through type display mounted on a helmet of a pilot so that the virtual images is superimposed on the actual field of vision.