A mirror surface for deflecting an incident light beam is inclined to the axis of rotation and rotated for scanning the light beam. The incident light beam is applied to the mirror surface along the axis of rotation, and a reflected light beam is continuously deflected by the rotating mirror surface to scan a surface. When the incident light beam has an elliptical cross section in a direction normal to its optical axis, the cross-sectional shape of the reflected light beam varies due to the inclination of the mirror surface in response to rotation of the mirror surface. The varying shape of the reflected light beam obstructs proper reading and writing of an image with a light scanning device employing the above mirror surface. To avoid this problem, light beam shapers are provided in positions before and after the light beam is reflected by the mirror surface.
