PURPOSE: To prevent a lighting system from malfuncitoning caused by dew condensation on the surface of a sensor, in a lighting system using a reflection type photoelectric sensor as a detecting means.

CONSTITUTION: At the lower side of a lighting system 11, a reflection type photoelectric sensor is used as a switching means of the lighting system 11, and at the light projecting and receiving surface of the reflection type photoelectric sensor, a light projecting and receiving member 18 injects the light. By forming a hole in a rectangular form so as to permeate the received near infrared rays, and fitting a transparent plate to the above rectangular hole so as to cover the hole perfectly, a sensor detecting window 21 is formed. A dewing detector 22 is provided to the sensor detecting window 21 being exposed on the surface of the window 21, and a heating coil 23 to operate by the detecting signal of the dewing detector 22 so as to generate heat, and to remove the dewing on the surface of the sensor detecting window 21, is provided at the front and the rear sides of the above transparent plate, or inside the sensor detecting window.