PURPOSE: To prevent the bad influence on other optical elements by the reflection light from the light receiving surface of the optical strength detector by arranging the optical element to vary the detection light varied to a first direction to a second direction and to converge the light.

CONSTITUTION: The parallel rays of light made incident to a partial lens 12 varies toward the focus passing the center of both convex lens and becomes converging light. By this actuation, the intensity detection light 11 of the first direction of A is varied to the second direction of B and is converged in an optical strength detector 13. Therefore, reflection light 19 from the incident plane of a glass cover 16 and reflection light 20 fram the light receiving surface of photodiode 17 of the intensity detection light 11 reflect in the different direction from the optical axis of the intensity detection light 11 and each reflection light 19 and 20 return and optical path of the intensity detection light 11. The intrusion of the reflection light as noise in a photometric sensor 9 after passing the optical path of data signal detection light 7 can be easily prevented.