To detect an object over a wider detecting angle range by providing an optical element having a focused lens and further a lens in which a portion of a reflection light is diverged.

A transmitter 12 provided in a sensor has a light source 20 and an optical system and a light beam 21 of the light source 20 is directed to a cylindrical lens 24 after a condensing lens is focused. The cylindrical lens 24 is a diverging lens diverging a light in one flat surface and a light is focused as such on a vertical flat surface but the light is diverged on the other flat surfaces. Therefore, a wide light beam 21 diverged from the cylindrical lens 24 irradiates an object and it is reflected toward a light receiver 14 at the same angle as an angle of incidence as a wider reflection light beam than a reflection light returning to the sensor. Accordingly, a detecting range by the light receiver 14 is increased and the sensor can detect the object over a wider detecting angle range.