Immediately before a robot 20 starts to move at a high speed, a monitoring area 53 is expanded in a returning direction Y, and absence of an obstacle in the monitoring area 53 is confirmed. Reagents which react together to generate steam when in mutual contact are mutually separated by a barrier, and disposed in the first chamber. In operation, the input stage receives an input current and the pair of complementary source followers receives a first current source and a second current source. Finally, an activation signal for an illumination source of the vehicle is issued when the ambient brightness drops below a predetermined brightness value and the presence of an authorized mobile identification transmitter is detected in the approach zone.