PURPOSE: To discriminate flickering of a lamp even in the case of direct exposure to the sunlight by providing a shutter which intercepts incident light transmitted through a lens or is opened so that light of the lamp is radiated through the lens.

CONSTITUTION: When a solenoid type electromagnet 13 is energized, a driving piece 10 is attracted against a spring 12 to close a shutter 6. At this time, light made incident through a lens 3 is intercepted by shutter pieces 7a and 7b, and the glitter of the lens 3 due to internal reflection disappears. When the electromagnet 13 is not energized, the driving piece 10 is attracted by the spring 12. and shutter pieces 7a and 7b are placed in the open position, and light from a lamp 4 is radiated to the outside through the lens 3. Consequently, the shutter 6 is controlled so as to be open at the time of lighting of the lamp 4 and be closed at the time or extinction of the lamp 4, thereby distinctly distinguishing between lighting and extinction of the lamp even in the case of direct irradiation with strong light like the sunlight.