PURPOSE: To determine the distance to a body geometrically and to determine the inclination of the surface of the body by using the information of distances from light receiving elements of three or more, by projecting light on the body continuously and periodically with an angle being changed, while detecting the changing times of the output signals of the light receiving elements regardless of the state of the surface of the body and the like.

CONSTITUTION: A sensor is constituted of a light emitting element L, a light receiving element R, a disc C having a slits, which is rotated by a motor M and a period detector T for the disc C. Light is made to pass the slit S and projected on a body G. The disc C is continuously rotated and the projection angle α of the light on the body G is periodically changed. The light receiving element R is sensitive to the reflected light from a specified direction among the light rays diffused by the surface of the body G. Therefore, based on the time when the reflected light is captured by the light receiving element R, the rotary angle of the disc is detected. The distance to the body is determined from the relationship between a geometrically predetermined rotary angle and the distance. At this time, when three or more elements R and detectors T are used, the inclination of the surface of the body can be determined together with the distance information based upon these distance informations.