This invention is one kind may supply automatically changes the illumination auxiliary the auxiliary lamp, is equipped with a control circuit in the headlight, this control circuit is contains has a microprocessor and one side examines to the angle knows the unit; This lateral angle examines knows can  the response march forward vehicles' lateral angle to give the microprocessor, after microprocessor computation actual corner, controls the auxiliary lamp photo source control end to open shuts, so, when the vehicles make a turn, then examines knows opens the auxiliary lamp, illuminates the vehicle ventral turning, enhances the tortuous path to go at night the time security.