PURPOSE: To obtain an automated active emitter and sensor system for inter- vehicle distance measurement and inter-automobile communication on highway.

CONSTITUTION: A preferable system comprises a pair of sensors 21, 22 arranged, while spaced apart from each other, on the front of each automobile in order to recognize the three-dimensional depth, two temporarily modulated emitters 23, 24 arranged on the rear of each automobile for the purpose of redundancy and inter-automobile communication, and temporarily modulated emitters 25 arranged at an interval along a highway for the purpose of communication from the highway to an automobile. The emitter transmits a radiation of infrared wavelength of 1μm, for example, which can be detected with a low cost detector and it is modulated temporarily in order to transmit a binary code. Consequently, S/N ratio is enhanced, clutter is removed and the operational range is enlarged.