A Risley scanner optics using a pair of revolving prisms is studied as a mechanically robust beam steering device of LiDAR (light detection and ranging) for automatic driving systems. Field of view of more than 100° (optical angle, full scale) is possible by using prisms of 30° for the wedge angles. Due to the nature of the Risley scan pattern, the optics is expected to have a high-density number of resolvable spots in the middle of the eyesight, while sparse but sensitive dynamic visions near the fringe of the sight.