The invention provides a stop lamp lighting controller able to improve durability of a relay while unnecessary automatic turning on and off are avoided. A stop lamp is lit through a main line at a gentle braking time. At a sudden braking time, the stop lamp is switched on and off by disconnecting and connecting the main line in a predetermined period. At a breakdown time of the main line, the main line is switched to a subline and a lighting function of the stop lamp is secured. The main line is formed when both a first relay and a second relay are in a de-energizing state. The main line is disconnected and connected by periodically opening and closing the first relay. The main line is switched to the subline by energizing the second relay.