One of minimizing the accident of car collisions from behind is to improve the stop-lamp visibility, and there has been many research on this field. Various methods have been proposed, which are the intensity enhancement of the stop-lamps, the enlargement of their sizes, and the installation of the additional. The intensity enhancement method is the most effective one, however, their brigthtness may annoy the drivers on the car behind， specially at slow-speed cruising or at a traffic jam during the night. By using the system which we built, the following improvements have been obtained; ① By changing the intensity of the stop-lamps, the visibility can be improved, and at the same time dazzling to drivers on the car behind can be avoided. ②The intensity of the stop-lamps can be adjusted by not the hardwares but the software programs.