PURPOSE: To enable switching between low beam and high beam by one luminous filament by disposing a liquid crystal screen on a converging lens surface and controlling the penetrating property of light on the liquid crystal screen.

CONSTITUTION: A first converging lens part 3 for radiating a low beam is provided in the upper front of a reflecting surface 2, a second converging lens part 4 for radiating a high beam is provided under said first part, and a liquid crystal screen 5 which is changed from the transparent state to the translucent state by application of a control voltage to prevent the radiation of the high beam is provided on the surface of the second converging lens part. Thus, the first converging lens part 3 can penetrate the light sent frontward from the reflecting surface 2 and radiate a low beam a2 which is a light dispersed in a wide range of the front, but a high beam b2 which is a focused light from the second converging lens part 4 is prevented by changing the liquid crystal screen 5 to the translucent state. Hence, the switching between low beam and high beam can be carried out by one luminous filament.